Bought this after being diagnosed with severe obstructive sleep apnea following an over-night study. The little alarm beep is perfect for me as it is loud enough to wake me but not so loud as to disturb others; I do wake rather easily though. It could be a problem for deep sleepers who have difficulty waking. The directions/functions are intuitive, so after going thru instructions a time or two, see youtube, "How to record overnight oximetry data", it was not a problem accessing the menu and setting up perimeters for heart rate and O2 sat levels, etc. More than anything, this gadget gave me assurance that what I initially believed to be true about my case of OSA is indeed true, caused by allergies/sinus issues, not some deeper medical issue as I was lead to believe.
The finger probe is a little uncomfortable to wear all night long; I'm conscience of the light-moderate pressure and it's rubbery, warm, sweaty and distracting feel...but it's tolerable. The big thing for me is how convenient it is as I can always put the monitor on if I'm concerned that a medication or high pollen levels or allergens could be tilting factors towards experiencing more apnea and therefore, can take measures and precautions. I haven't used the software to download anything...I just basically use it as a wearable pulse-oximeter with an alert that sats may be dropping lower than they should.

It basically works as advertised. I bought it to integrate into a CPAC monitoring program, SleepHead.
The battery, which is rechargeable, easily lasts two to three nights between charges. The finger out alarm will wake me after awhile. While I did check out the included software, SleepyHead has its own report driver to download the saved data.

The Bad
The front push button is large and sensitive. You can easily turn it on by laying it on its face. Its menu driven and to change any setting you need to hold the button down a little longer than momentary. That prevents unwanted changes from occurring.
While powered on during the night it looses about 1 min per 6 to 8 hours. Powered off for the next 16 hours, it looses about 6 minutes.
The finger monitoring pad if placed all the way down on a large finger will cause pain in that digit in the morning. I either switch it during pain medication time during the night or place it on my smaller fingers.

The GOOD.
Battery charge will easily go 3 nights.
Data capture is excellent and SleepyHead has drivers that will connect right to it.
The finger monitoring pad fits on easy and takes a large effort to accidentally remove it from your finger at night.

Correction:

The device is accurate in time keeping, every time I connected it to my computer, the computer would change the time in it to match the computers time. Found a little box that turned that feature off.

Excellent product. The engineering is spectacular, but unfortunately it is not reflected in the manual. The small CD disk loaded the reporting software to my Windows 10 computer with no problem. The reports from this software are better than what my doctor's office obtains. It's easy to justify the purchase -- your insurance co-pay for two tests covers the price (if you have bad insurance this product is definitely the way to go). For instance, you have an initial overnight study then get a CPAP machine then you need another study -- BINGO, you just broke even. The report I like the best is where an hour of data is displayed in 8 strips for an entire night. You will need to "play" with the software since there are several report settings.The manual does not tell you what the results mean. Your doctor should do that. But, just as a ballpark figure: during the night, less than 7% of readings should be below 88%. Also, a little masking tape keeps the finger probe in place for the night. Data for each study is saved as a separate sequential ascii file for those with an IT background.

I bought this to get an idea how my oxygen and pulse fluctuate overnight. I believe it to be very accurate as it exactly mirrored a more portable Pulse/Ox meter I had on my other finger when testing.

There are two main ways this needs to improve.

First, this is clearly for long term measuring but the instruction booklet says not to keep in on your finger for more than an hour or two (I forget which) which is impossible if you're sleeping. The reason is your finger sweats inside the sealed rubber and it's like you kept your finger in water all night. They could easily have put air holes in the side to ventilate your finger- hospitals have similar ones that can stay on your finger indefinitely without this problem.

Second, I am a computer/software expert but still found the software to be less than intuitive, I believe most people will find it difficult to use. It would benefit from better instructions and better software.

However other than that I did find it very helpful, and yes my finger got all nasty for a while but it cleared up once exposed to air again in the morning.

Also- wish this used a Micro-USB port that has been standard for years and not the older, much less popular, Mini-USB connection that hasn't been used on a phone in 6+ years if I had to guess. Annoying to have to keep a second wire just to charge it. (Charging wire is included with the device.)

The CMS oximeter works well. My wife and I use it to monitor our sleep to get baseline oximetry readings. I intend to compare it when I try different snoring aids. This unit is handy to use and allows the night's oxygen and heart rate to be recorded using the windows software that comes with the unit. While snoring is annoying to your sleep partner, oxygen absorption and heart rate is important for your health. The software is not the easiest to use, but works well once you figure it out. The wrist unit is not to uncomfortable; and the piece that fits on your finger is flexible but snug enough to stay on during sleep. The instructions say that finger nail polish will distort the readings, but my wife didn't have a problem. I found that although the battery charge lasts through the night, I have to reset the time and date, and recharge the unit before each use.