After extensive research about different running watch and fitness tracker manufacturers and models, I wore the Garmin Forerunner 35 and the Fitbit Charge 3 on the same wrist for several days and conducted a detailed comparative analysis of their data (think spreadsheets with multiple tabs and graphs). The metrics I looked at included daily resting heart rate, steps, calories, distance, and sleep. I also examined activity data, i.e., distance, average heart rate, average pace, and calories during my runs and dog walks.

At the end of the day, the two fitness trackers gave fairly consistent data, with variance usually at or below 5%, an acceptable margin all things considered. However, after this experience, and despite LOVING the Forerunner 35's built-in GPS (which the Charge 3 lacks), I chose to go with the Fitbit for three reasons:

1) The Fitbit has more frequent heart rate sampling -- the sensors measure it every 5 seconds while resting, compared to what appeared to be measurements every minute(?) for the Garmin. I realized this because I noticed that the Fitbit's green LEDs were always on, but they were frequently off (not flashing) on the Garmin and would only come on periodically. Presumably this is to save battery life on the Forerunner.

Practically speaking, this meant that stats over a longer period of time (such as average heart rate during a 45-minute run, or resting heart rate for the day) were fairly comparable between the two. But if I wanted to get my current heart rate at a glance, the Fitbit was usually spot on as soon as I looked at the device, whereas the Garmin was sometimes 30 bpm too high or too low. (I am fairly in tune with my resting heart rate so know the Fitbit was accurate in these cases and the Garmin was off -- especially because once the Garmin told me it was 42 bpm, and I know my resting heart rate is more in the high 50s.)

Once the Forerunner realized I was trying to look at heart rate data, it would start flashing its LEDs and the number would then either decrease or increase to pretty much match what the Fitbit was showing me from the get-go. This is a minor issue that wouldn't compromise the integrity of heart rate data in the long run -- after all, relative trends over time are what these sorts of devices are best for -- but I got annoyed by seeing incorrect numbers and having to wait 10-15 seconds for the Forerunner to adjust.

2) The Forerunner's sleep tracking wasn't as accurate as the Fitbit. I think this comes down to an issue of sensor sensitivity and/or how algorithms interpret the sensor data on the back end. Basically, the Forerunner was consistently telling me that I was getting anywhere from 20-45 minutes more sleep than the Fitbit every night. I have a good sense of knowing how I feel with N hours of sleep, and I think the Forerunner was overestimating.

Further evidence for this hypothesis is that one night, I got up around 4 a.m. to go to the bathroom and check on my dog. The next morning, this few minutes of "awake" time and the steps I took were reflected in my Fitbit data, but not the Garmin data. Basically, the Forerunner somehow missed that I woke up, got out of bed and walked to the bathroom down the hall, walked to the living room, and walked back to bed. The missing steps are not important to me, but how did the device not catch on to the fact that I was awake? Surely it should've picked up on that based on my heart rate and movement.

3) The Garmin's step counting was overzealous. The Forerunner 35 consistently told me I was doing more steps per day than the Charge 3, sometimes only by 200-300 steps but other times by 800-900 steps. That's an almost 10% margin if you're aiming for 10,000 steps per day.

I'm guessing one reason for this is that the Fitbit allows you to adjust settings in the app for wear on your dominant vs. non-dominant wrist, the former resulting in algorithms that err on the side of excluding movements that may not be steps. Garmin's devices do not appear to have this setting, meaning they are probably overcounting by interpreting some non-step movements as steps.

4) I'm a fairly petite person (5'2", 120 lbs) and the Forerunner 35 was a bit too big for my taste. The screen's length pretty much occupied the entirety of my wrist width, and it was pretty thick too. I occasionally had trouble pulling my sleeves up if my clothes were fitted, such as with long-sleeved base layers -- which I would wear while running, precisely when I wanted to see the watch. Obviously an issue of preference, but I found it mildly annoying.

In conclusion, I would say that none of these is a deal breaker if what you really want out of the Forerunner is a decent GPS running watch. Its built-in GPS is truly wonderful, the auto-lap feature is super convenient, and the customizable data fields for workouts are fantastically brilliant. It's uber functional without any superfluous or overly complicated frills, and I especially love that it has the day of the week and date shown on its always-on display. Battery life is competitive, especially for a GPS watch. However, when push comes to shove, I personally prefer more reliable data. I couldn't keep using it and raising an eyebrow every time the information the device gave me didn't match what I know about my own body.

While I was in the military from 1895 till 2005 I was in excellent shape. I was doing about 4 hrs of progressive weight training/week and getting 7.5 hrs/week of very high intensity cardio. When I retired, I was probably in the best physical condition of my life, at 6% body fat. I was 51, then. After I retired, for the first few of years, I maintained a gym membership and kept up my training. By 2010, I was working in my consulting business, and I began teaching part time at a local university. More time on my ass and less time in the gym. In 2013, I began teaching full time, and I became almost totally sedentary. About the only exercise I was getting was walking across campus between classes. Just before Christmas, I calculated my body fat percentage using the Navy method. At 5'8" and 178 lbs I found myself to be 29% body fat and obese! That did it for me. I realized I had to start to get back into shape, and I realized that it would be a lot harder now at 65 than it was when I was in my 20s.

I have never been much of a distance runner/jogger. In the Navy, I ran my 3 miles a year for my two physical readiness tests, and that was about all the running I actually did (even though I was a sprinter in college). It also occurred to me that I probably just couldn't jump on a Stairmaster, and workout at 175 bpm heart rate for 90 min, either. So, with the recommendation of my internist, I decided to start increasing my activity by walking. We live in a subdivision on a street that is an oval of exactly 1/2 mile in length (I drove around it eight times and it really is exactly 1/2 mile). I started walking around my street on Dec 26. I started going around twice (i mile), then I increased the distance by a lap a day, until I was up to 10 laps on Jan 3 (I took Jan 1 off). Since then I had been walking between 8 and 10 laps daily, trying to increase my pace as I went. Somehow, I knew I wasn't getting enough feedback from just the mileage/time calculations. Back when I was working out in gyms, I always wore a chest strap, with one of the more advanced Polar watches. Now that it is over 10 years later, I explored more modern technology, in the age of FitBit and Apple Watches.

Actual review starts here: One of the first decisions I made about getting an exercise watch, was that it would need to have GPS, since I have resigned myself to a walking regimen until I get my weight under control, and I regain some of my cardiovascular endurance. I also wanted a watch that used ANT + as its transmission system, because I knew that at some time I would want to add a chest strap for more accurate heart rate measurements (I purchased a Powr Labs strap that arrived today, more about that coming up). I also wanted the watch to be water resistant enough to allow me to swim (This is south Florida, and in the summer, it is a lot easier to do laps in a pool than it is to even walk, and by Summer, I will probably need to change to an activity that will allow me to increase my heart rate above the aerobic zone). The final thing was that the watch needed to be easy to read in a number of different lighting conditions. As I was purusing the various devices here at Amazon, I was immediately struck by the Garmin watch. Ergonomically it appeared to fit exactly the way I would want a watch to fit (I haven't worn a watch in over 20 years), and the way the contrast is set to make the LCD display easier to read with more intense light, it appeared to be perfect for outdoor use in Florida. After reading a number of reviews, that suggested it was a good watch (but not great) at $200, I figured that for under $100 it was probably more than enough to satisfy my needs.

The watch came the other day, and I spent about two hours reading the manual and playing with the features. I took the watch outside, selected the "Walk" activity and the watch set the time and date through the GPS signal (None of the Polars I had previously owned did anything like that, and the most annoying thing about those watches was setting date and time). Yesterday was my first day actually using the watch. Before I left for school, I did four laps around my street, and sure enough, the watch registered 4.1 miles ( I stopped it after walking up my driveway). It also had my HR average at 122 bpm, which seemed reasonable to me. At school, the class I taught yesterday was in the library, which is about a half mile from the building in which I have an office. Since "walking" is to be my fitness thing, I walked to and from class from my office building. After I got home, I walked another two laps around my street. After dinner, I synched the watch to my iPhone. After the synch, all of the activities I did since I began wearing the watch were displayed. I guess I'm still fascinated by the GPS thing, and when I tapped each of the saved exercises, I was treated to a GPS map of my actual walking path. The repeated oval around my street wasn't too interesting, but at school I took two different paths to and from the library, and it was very cool to see them clearly defined on the map display.

Today is my day off from school, so this morning I set out walk my 10 laps around my street oval. Just before I left the house, the Amazon Prime truck arrived dropping off Powr Labs ANT + chest strap. I took some time to synch the strap to the watch, and then set out on my walk. I walked eight laps, then paused to remove the strap so that I could proceed with just the watch measuring my HR, so I could make some "in the ballpark" comparisons. After two more laps, I went into the house and synched the watch to the iPhone. Of course, I got the same boring GPS map of the "circle" on which I live, but the thing I was most interested in was how close the average HR measurements were between the watch and the chest strap. For the chest strap, the eight lap HR average was 130 bpm (I try to walk at a little over 3.5 mph pace), and the two lap average for the watch alone was 132 bpm. As far as I can tell, the physiological variables were probably more noisy than the actual differences between the measurements, and, at least for my wrist physiology, the watch is probably "close enough for Government work".

So, in conclusion, all I can say is that I really love this watch. It does way more than I really need it to, and things I need it to do it does exceptionally well. If you are a competing tri-athlete, you may need something more powerful and complicated, but for me, and I'm sure the many people who want to invest in a product that will help get them off there asses, for the cost, there really isn't a lot that competes well with the Garmin Forerunner 35.

I've had this watch for about a month and a half now, and I love it!!! I had the Forerunner 15 (which is also a great watch) before this, and I like the 35 even better! It is definitely slimmer than the 15 and looks more like a smart watch than just a GPS watch. It is not touch screen - it has the same 4 buttons as the 15, and the interface is similar. The 35 has a bigger face and the time is displayed in white with the background black which makes it easier to read in the dark (it does still have a backlight button like the 15). I wear my watch all day, but not at night. It's supposed to do sleep tracking if you wear it while you sleep, but it bothers me to have something on my wrist while I sleep, so I haven't tested that feature. I think the step tracking is accurate - it seems comparable to what my 15 was calculating. The GPS is very accurate - within .05 of a mile I would say. If I'm running on a measured course, it usually is a bit under what the course is supposed to be, but that's probably because I'm running as close to the inside as possible making the distance I actually ran a bit shorter than what the course is supposed to be. The 35 offers several features that the 15 does not have: smartphone notifications, bluetooth connectivity, displaying the weather, and heart rate. Starting with the smartphone notifications: it is pretty simple to set this us - just connect via bluetooth through the garmin connect app (I have a Samsung Galaxy S4 and it was easy to set up and works well). There is a setting where you can set which apps you get notifications from and you can set it to beep or vibrate or both. I have mine set to vibrate and it works perfectly. You can NOT send messages from the watch - it ONLY READS notifications. If you want to send messages or make calls from your watch, this is not the watch for you. However, you can answer/reject a phone call from your watch. This has been surprisingly useful - if my phone is in my bag, across the room, or somewhere else, I can answer the call from my wrist then look for the phone so I don't miss the call. Also, I keep my phone on silent all the time, so its nice to know when I get a message and not disturb others. There is a do not disturb mode - the watch won't vibrate/beep which comes in handy sometimes. On to bluetooth connectivity: You don't have to plug in your watch to sync it with garmin connect! It will automatically sync with your phone when bluetooth is enabled! I didn't think that this would be a big deal, but now that I have it, I don't think I'll buy another watch without it - its just so convenient. Weather: It will display the weather, but you have to have the GPS on your phone turned on (I don't leave the GPS on my phone on, so I don't use the weather feature). I set it up at first and turned on the GPS just to see what it looked like, and its pretty nice - it gives you hourly temperatures and rain chances. Heart rate monitor: I think I like the idea that it has a hr monitor more than I actually look at it. There is an option to turn the hr monitor off if you want (I assume it would save battery). It calculates your average resting hr which is nice (I haven't tested its accuracy, but the numbers seem right). It also gets your hr during a run/workout which is nice, but I rarely look at it. One final feature that may be the best thing about this watch - it does "find my phone." You have to have it connected up by bluetooth and be in range (which is surprisingly far and can even go through a wall/door). When you select find my phone on the watch, it makes your phone ring (even if its on silent), vibrate, and the flash for the camera blinks. I haven't tried it with my phone turned off, but I don't think that would work since it has to be bluetooth connected. I almost forgot about music control! This is a great feature that lets you play/pause/skip. I don't use it because I don't listen to music when I run, but it works well - I played with it when I first go it. Overall, I love this watch and highly recommend it!

Pros:
Accurate GPS
HR Monitor
Phone notifications/answer calls
Bluetooth connectivity - automatically syncs
"find my phone"
control music from it
Interface and overall look of the watch is much sleeker than the previous forerunner models which have a very sporty look

Cons:
Can't send a text from the watch
Have to have your phone's GPS turned on the use the weather feature

There is nothing that the watch does poorly, the cons are just features that would be nice if it had them.
Another quick note: Battery Life - It has not been an issue for me. I charge my watch every night, but it usually still has 2/3 bars of battery when I plug it in. I run every morning for 30-75 minutes with the GPS on which is the primary loss of battery. If I don't run, it stays at 3 bars the whole day. I think the HR Monitor can drain the battery too, so if you wanted you could turn that off.

I wanted a watch for fitness tracking that has a heart rate monitor
I was wanting reliable readings and long battery life . This Garmin is a pretty good entry level fitness tracker and I trust Garmin products for toughness and design for my own personal use.

Synopsis: Overall, this is a good, basic running/ fitness watch that makes a nod at also being a smart watch. There is nothing flashy here. The watch doesn't do color, just back and silver/white on the display. For those who have used or who remember the traditional Kindles, this is actually pretty nice in terms of contrast as it is easy to ready in low light and high light conditions. In the dark, you still need the light from the lighting button. Unless you are a pro/ elite level runner who will use the advanced features of the higher end watch offerings from Garmin or their competitors, or are someone who doesn't mind paying an absurd amount for a the latest tech gadget, this watch is more than adequate when paired with external sensors such as the HRM Run. As you read this, please bear in mind that I haven't had the opportunity to run the higher end models, so my only points of comparison are the spec sheets and the price points. I will try to avoid providing second hand anecdotal evidence for or against them.

What's Good:
-- The weight. This watch is very light. Unlike my dive watches and other larger, necessarily robust watches, this guy is light enough that I don't feel a need to take it off to type or when doing wood work (both activities that involve repetitive motions that become annoying with larger watches on. For those who mind having something heavy on your wrist during a run, that won't be an issue with this watch.
-- The Band. The silicon band that comes with the watch seems to be robust and is stretchy and comfortable. I have had sport watches in the past that became uncomfortable in hot conditions after a while as moisture built up under the bands making them itchy or painful. To date, I have had no such problems with this watch. I also like the securing ring on the band which has a tooth on the inside to lock it into one of the fitment holes. The stretchiness is important as you need the watch snug/tight to adequately place the optical heart rate monitor.
-- The Smartwatch functions. I don't own an apple watch (which wouldn't work with my phone anyway) or a Gear S3, so I don't have a basis for first hand comparison. However, I have observed the frustration of my friends and family with such devices when trying to use them for input tasks (two way communications with the cellular device.) This watch passes on notifications from your phone, but you have no ability to respond with it. For me, this is the best of both worlds. I get to keep situational awareness while avoiding getting caught up in the minutia of responding with a yet smaller computer interface. This is a personal preference, but I do like the way it works. It is also nice that notifications turn off during a run.
-- The interface. The UI (User Interface) is menu driven. It took me only a few minutes to get used to it, so it has to be fairly simple. Overall, it is intuitive once you absorb the designer's logic, you just have to be patient. It does not have a touch screen, so you have to use the buttons. This isn't a problem for me.
-- The GPS. Because this is a lower end offering, the watch only uses the GPS constellation and not the GLONASS constellation (Russian GPS). As a result link up times are a little slower and accuracy can be degraded as the US places a mandatory limit on how accurate civilian GPS instruments can be (its a strategic thing.) Overall, this watch isn't too bad. At the end of my recent runs, the watch is generally off by about .03 to .05 miles from my phone which uses both locating systems and you can see the differences in the map. Part of this is, I am sure, due to the frequency of updates which is not user changeable unlike on the higher end devices (I would love to minimize the time between fixes.)
-- External Sensors. You can still use external sensors with this watch. I love this feature as I prefer the HRM Run over the watch which has its own accelerometer. This becomes very nice when I'm pushing my daughter in a running stroller. For bikers, you could also use a cadence sensor.
-- Movement Tracker. I like to track steps. As a teacher though, I take everything out of my pockets when I get in front of a class so I don't fidget with it, so its nice that the phone will continue tracking for me. Its also nice that it will tell me if I've been sitting too long. This is good for two reasons. Research shows that you start to lose focus and effectiveness after about 50 minutes of continuous concentration, so its a reminder to take a break (the movement bar seems to ping after about 45 to 50 minutes). Its also a great reminder to remain active instead of just sitting there like a lump on a log.
-- Battery life. The phone is advertised as having up to a 13 day battery life. I haven't seen it. However, it does seem to last about 5 days with workouts which draw significantly more power than standard operation.
-- Charging. The charging of this device is impressive. My first forerunner, the venerable F405, had to charge on a cradle that was poorly designed and didn't positively engage the device. Over time, the connections would degrade and eventually stop working. The new version uses a clip that actively clamps onto the watch. Even with oxidation, it should last a long time. The other part of the equation is the speed of charging. In this aspect, the watch charges very quickly. My personal experience is that a full charge takes less than 1 hour. So if I'm at my desk and notice that my watch is low, I can put it on to charge and have it back on my wrist in time for my next break.

What's not?
-- User control. The sacrifice you make to get a robust watch is that you sacrifice control. You can still adjust view fields on the exercise screens, but can't change how often the watch takes position fixes which would affect accuracy. There are some other little niggly bits of control that are sacrificed as well, but they are well hidden. Now, that having been said, how much control does the average user really need? If you ask the fruit company, they will tell you not much.
-- Accuracy. As mentioned with the pros, the watch is not quite as accurate as I have come to expect from my phone. However, it is within the tolerance of the system so really, how much are you missing?
-- User feedback. The watch does not provide the same level of feedback as the higher level watches. Such esoteric values as VO2, Lactate threshold, expected recover time, and foot contact time simply are not measured. Now, here's the thing. If you are an elite level athlete or a professional, or have a personal coach that actually cares about this stuff, you might care. If you are an every day runner or biker out for fitness and fun or a weekend warrior out to train for your local half, do you really need that extra information and will it be of benefit to you? This is a question you have to ask yourself. My answer was clearly no. Now that having been said, the higher end watches all rely on the chest strap sensor to develop those metrics. Would it be possible for Garmin to move the calculation muscle to your paired analysis device (computer or smart phone)? Well, the answer is that there is nothing technically in the way, so clearly it is a selling point for their higher end lines. Will it show up on Garmin Connect in the future? Who knows.
-- Limited activities. The watch has limited workout options: Run outdoor, Run indoor, Bike, Cardio, and Walk. If you are looking for something that will track your cross fit WOD, this may not be your baby. Nor is it really designed to track golf, basketball, Frisbee golf, ultimate Frisbee or weight lifting as separate activities. Of course, most of the devices that are built around that desired capability are not reported to work well in that application. If you really want something that has specialized tracking capabilities for a wide variety of sports, by all means, pay for the higher end models.
-- Garmin Connect. Perhaps I'm just getting used to it, but Garmin Connect has some issues in the way that it appears on my phone. It tends to be difficult to navigate and can be hard to get it to sync.
-- Only two potential watch faces. There are two built in watch faces and there are no options to be able to create your own. This would be worse if I cared more, but I personally like the simple, in your face faces that are standard with the watch. The higher end watches have infinitely adjustable faces.

Wrap up. Over all, I am very happy with this watch. It is the rare blend of having most of the features that I wanted and all of the capabilities that I need, while maintaining a reasonable price point without having to turn to the factory reconditioned items that may have been a lemon to begin with. I highly recommend this watch/ fitness tracker. If you don't believe me, check out the consumer reports review of this watch.