Another Whoop user and it works very well for me as a sleep tracker (and otherwise). For me, its uncanny how good it is at recognizing when sleep starts and ends. It even handles my regular old man middle of the night potty trips. As for the intra-sleep data the app reports, I’m asleep so I don’t know what’s really happening with my REM sleep et al but the basic night’s score matches well with how I feel.
Its also easy and unobtrusive to wear at night. The battery lasts about 4-5 days and you charge it with a battery pack while wearing it so its very easy to just keep it on 24/7. I don’t know its there until I want it to be there.