I have had one of these Mr. Coffee hot beverage warmers for many years. I used it daily. This hot beverage warmer is very safe to own and operate. It is worth every penny, as it will last you for many years.
I will give some tips here that will ensure that your favorite hot be erage stays hot for hours on end:
First, consider your coffee cup or mug.
If you are older, you may remember the thick ceramic mugs that donut shops and truck stops used to use.
Look for these, even used ones in thrift stores. These thick ceramic mugs are unmatched for retaining heat. Yes, they can be a little on the heavy side. And no, they may not look chic. Np.
Also, look for cups/mugs with nice flat bottoms. This will ensure that your mugs make a nice full contact with your warmer. This equals hotter beverage. Avoid cups or mugs that have a ridged base. These ridged cup bottoms actually have a cooling effect on your hot beverage.
Next, keep a glass/ceramic cup saucer on top of your cup while not sipping. This will ensure that your beverage stays hot and steamy for hours on end.
The glass/ceramic saucer on top keeps the hot steam in your cup. This helps your beverage stay hot, just like a blanket keeps you warm. Also, the heavy weight of a glass/ceramic cup saucer on top presses your cup down into the warmer. This really helps your beverage stay nice and hot too.
This Mr Coffee beverage warmer is really a mini hot plate. If you follow the tips above, your beverage will stay nice and hot for hours on end.
The only thing that I don't like about this beverage warmer is this:
Mr Coffee chooses to paint the hot plate with flat black paint. It won't take long for your new coffee warmer plate to get all scratched up, making your warmer look old and unsightly.
You could repaint the hot plate, but this is a very temporary solution at best.
The underlying material seems to be a silvery aluminium. So the paint scratches look really bad. Instead of repainting the hot plate, I would suggest getting some paint remover, and just remove all the paint on the hot plate. Polish up and buff the bare hot plate. This will ensure that your warmer looks nice for years to come. And, by removing the paint on the hot plate, this makes the heating element be even hotter, as no paint will get between your cup and the heating element. Also, remember to hit your warmer with one of those waxing/cleaning cloths now and then.
A word of warning: Never, EVER touch the hot plate when the warmer is turned on. You will get a severe burn. The same goes for children also, obviously.
This beverage warmer really does the trick. Especially if you follow the simple tips above. Clink clink. Enjoy!
Oh, one more thing: Make sure that your beverage is piping hot BEFORE you place your mug on this warmer. This is a beverage warmer, not a beverage heater upper. I pop my coffee mug in the microwave for 30 seconds before placing the mug on the warmer. This helps a lot.

I wasn't sure this would be appropriate for my tiny work area. I have a large closet I use half for a small desk to work at home. I use one shelf for my necessities. It can get chilly and I bought this for keeping tea warm. It does work but after trying several of my cups I found the one with the round widest bottom worked best. Some cups that are not shaped with a big enough bottom surface probably won't warm as well. That is why I subtracted 1 star. I take a plastic yogrt container top and cover my cup and it gets nicely warmed. I recommend but make sure you have a cup with a full coverage bottom surface.

I work from home and keeping a warm cup of bliss is a must. I ordered this back in 2014 and three years later it is still a worthy purchase and one that has made life a little bit sweeter.

BASICS
So it's not the prettiest thing ever. Black, kinda shiny plastic with a cord that is about 65 inches. On/Off switch is pretty basic and while the indicator light isn't that bright and I can't always tell if it's on or off (what's the point then), it is easy to see as it is located on the top.

WHAT FITS ON IT
I measure the "seat" for mugs to be about 3 3/8".

Yes, it fits Starbucks "You Are Here" Collectors mugs. Yes, you can use mugs that DO NOT have a flat bottom and in my experience it heats up great. I have never felt the need for a flat bottom mug or even a cover for my mug to keep the heat in as the warmer does a great job at that.

No, it does not easily fit Bath & Body Works 3-Wick Candles, although they can still sit on top of the lip and heat up. I've done this before and despite the space between the candle and the seat of the warmer, the wax will liquify. The only issue with these types of warmers and large candles is that they will heat from the bottom-up, so you will not smell your candle until it is almost completely liquid. By then it's been hours and me-time is over and done. Not to mention that doing so will mean your wicks will have fallen into the hot liquid wax so don't plan on ever using those later! If you're looking for a more practical candle warmer, try one that heats from the top down so you can get your much needed aromatherapy on quickly. I've purchased the Candle Warmers Etc. Aurora Candle Warmer Lamp, Bronze which worked really well and fit the 4" bottom of the 3-Wick Candles, although at the time of writing this it is currently unavailable.

HEATING CAPABILITY
I have had great experience with the heat from my Mr. Coffee warmer. It literally brings back a cold cup of joe to really warm temperatures. I once left it on all day (lol my bad) with hot cocoa and when I came back it looked as if the liquid had all been baked off and I was left with gross dry cocoa crust. Yum?

I also went ahead to do you all a solid and got out my handy dandy EtekCity infrared thermometer gun and did some temperature measuring. After a while of having an empty mug on the heater, the bottom of the mug 145ºF and the warmer's base was 250ºF. I have no idea how that helps but there it is! All I can say is that it does the job of keeping my drinks nice and hot. :)

COMPARISON
The only warmer I have to compare this to is HEYANG Electric Coffee Mug Warmer and Beverage Warmer Waterproof Glass Panel Electric Heater Plate with 63 Inches Long Cord Great for Office Home . Great listing name. I got this as a Christmas gift this last year because I wanted a mug warmer that looked pretty enough to be out in the open like in the living room where people will see it. On/Off indicator light is on the side, which is okay I guess. (God forbid if I have to lean over a little to see if it's On.) Loved that it was completely flat and had no lip, but reviews said it was best used with flat bottom mugs. WHO HAS FLAT BOTTOM MUGS? I thought maybe they were just being picky. After all, people say that about Mr. Coffee but I totally disagree as it heats all my mugs just fine. But unfortunately I have to agree with the reviews for "HEYANG Electric Coffee Mug Warmer and Beverage Warmer Waterproof Glass Panel Electric Heater Plate with 63 Inches Long Cord Great for Office Home" and say that it's heating capability for my standard non-flat-bottom mugs isn't that great and I'm a little disappointed.

If you find a pretty one that works like Mr. Coffee does, please tell me in a comment!

I don't know what it is about hot drinks that I just cannot for the life of me remember to drink them until they are ice cold, but it has always been the main reason why I have iced drinks instead.

This has solved all of my problems. It's great and has kept my drinks warm literally all day. I will say that if you leave too little liquid in it when you have it on the heater it can be a little too hot and sometimes can taste a little burnt. But other than that it keeps the drink the perfect temperature all day which is amazing.

It has a red light that turns on when you flip the switch which is really helpful to make sure that it is off. There is a large protective ring around it so even someone as clumsy as me can't burn myself unless I really try lol. The cord is pretty long so it is able to reach far enough so it can sit anywhere comfortably on my desk.

The paint has chipped a little since I have gotten this but it hasn't really made any difference in the quality of the way it works but just keep it in mind.

Mr. Coffee mug warmer: As I use it, I will update this review. Cord is long (3.5 feet), the actual heating surface is 3 and 3/8 inches diameter, and it's well made and inexpensive. It turns on with a red light on the unit (unlike another brand that has the on/off switch on the AC electric cable). A superb substitute for schlepping my soups in with a thermos every day (hard to clean, extra work at home, etc.)

My goal: warm soup at my desk. I don't want an open flame (e.g. alcohol cook stove), or a very hot 750+ watt cooking element/hot plate. A small Crock pot is hard to eat from and wash--so, I thought this Mr. coffee might be what I want. I don't drink coffee, but could see using it for hot cocoa.

The test: I can put a room-temperature full 8 ounce Campbell's Soup--chicken noodle, to be exact--contents in an enamel-coated aluminum 12 ounce cup with lid, and in 30 minutes it's fairly heated and I could eat it, but in one hour, it's nice and toasty and ready to eat. It's hot enough that I cannot touch the bottom of the cup. I was concerned about the honest reviews that said this does not get hot enuogh--but after using daily for a week, it's mighty hot. I certainly cannot touch the warmer surface--it's far too hot. My office is not near a microwave, and this is a lifesaver for me. I may try canned stews next. I adore eating at my desk. A fellow office mate actually warms water--not to boiling, but very hot--over and hour and then dumps it from the cups into camping meal bags (cook in bag types, like Mountain house) and eats well every day. Sure, if someone had a microwave it's faster, but why challenge the entire office for microwave time in the grody kitchen room when you can set this out an 11AM and be eating well by noon.
Here's the exact cup I use, which fits the Mr Coffee well.

Coleman 12 Ounce Enamelware Coffee Mug (Blue)

Tips: The cup makes a big difference. I use an enamel Coleman aluminum cup, which holds one soup can well (not too close to the top), and conducts heat exquisitely. I have no clue is a hard and thick ceramic coffee mug would work. Also, I put a lid on the cup to hold heat, and so I don't get paperclips and junk in there while it "cooks". Lids reduce heating time by 18% (according to camping websites). I use a simple ceramic drink coaster that I had at home for my lid--any nonflammable lid would work. The lid helps. Also, the Coleman mug that I use is flat bottomed, thus using the entire heating element successfully. A curved bottom mug may not heat as well.

P.S> Okay, I just did Campbell's Vegetable Beef soup in it today, thick and I added no water, and it took about 1.5 hours to get fully hot. Still worked great, but clearly the thicker the soup, the longer the heating time. Also, the heating is most intense at the bottom of the mug or cup, so (1) stirring helps, and (2) a tall style ceramic mug or cup would not be as good as a squat one.

I bought a second one for home since I liked the first one so very much, and to test if the first one was a fluke and just extra hot or something. Guess what, no fluke. The first and second are equally as hot.

Postcript: just for kicks, I put tap water at room temperature in the blue Coleman cup for 60 minutes on the Mr Coffee warmer, and I couldn't even stick my finger in it at all. It was hot! Not boiling, for sure, but clearly hot. I wouldn't want it that hot to drink or to eat. And, so, I added an ice tea bag and took it off the Mr Coffee and drank tea. PLenty hot! Lovely! Bon appetite!