Update: I was wrong (Avoid! Shuts off if you have moderately low heart rate)
As an amazon seller myself I am here to admit I left a bad review based on my own ignorance. Originally this thing kept throwing a heart rate alarm and stopping when my heart rate was below 50bpm, then I couldn't get my blood oxygen level to change no matter how hard I tried. That is because I didn't read the manual (typical guy). Out of the box it is set to "spot check" and minimum heart rate of 50bpm. If you read the manual it tells you how to put it on your finger, hold the button and get into settings. I changed the minimum heart rate to 40bpm and reading to "continuous" and just like that everything worked great. There are a bunch of other settings as well. I had the distinct pleasure of watching my blood oxygen level dive during the wim hof breathing exercise.
Rating: 5 stars