Pretty cool product to be honest. Easy to use and it confirmed what I already thought - that my tiredness is not from sleep apnea. I don't snore and my wife says she hasn't ever heard me stop breathing but I don't sleep well. My doctor wanted to order a sleep test to the tune of $5,000 (or more) that insurance only pays a part of so I decided to try this first. While probably not 100% accurate, I would assume it is accurate enough to at least figure out my next step.
The other reviewer mentioned it was comfortable. I agree. After a few minutes you get used to it on your face. The only problem I saw was that I am a side sleeper so with it being on my cheek, it "mashed" into the pillow. I was worried it would fall off at night or bend away from my nose but it is on there pretty good so that was not a problem. It bent a bit when I laid down but I guess the pieces that are outside the nostrils were still working since I could see the red light when I would exhale (this stops after 20 minutes) even when I was on my side.
All in all, if you think you have apnea, I recommend trying this first. They are all the same (only thing like this in existence that I could tell) so find the cheapest deal you can. You dont get a "better" one from someone charging more.
Finally, they are meant to be used by doctors so there is no information in the packet that comes with it about what the codes mean. I had to Google them. 0 = No apnea, 1= Mild apnea, 2= Moderate apnea, and 3 = Severe apnea. I didn't have the same problem with needing to change the lighting to see mine like the other reviewer although it tends to fade over the space of a few hours. The correct way (based on what I could glean online) is to wake up, take it off, let it sit for 30 minutes, pull off the green sticky tape that covers the number and check the code.
Your mileage may vary, but this put my mind at ease and will let me explore other "why don't I sleep well" options without expensive overnight stays in a sleep center.