Why buy this ?
There are a wide variety of fitness trackers.  Some also track and monitor sleep quality. Here is one you might consider.
Fitbit Inspire HR Heart Rate & Fitness Tracker: The  is rather small and more comfortable to wear than some larger devices.  About $100.  Once again, research shoes that if you keep track of your exercise you are more apt to sustain a regular routine of exercise. This and similar products make that easier to do. Also, if you wear it during the night it will index slow wave and REM sleep. These devices have been popular.