i have one, been using it for around 4 months, in short im not convinced.
the biggest issue i have with it is that apparently i get a much harder workout cleaning my bike than i do from actually riding it. this comes down to fit and Whoop do say that the band doesnt fit everyone perfectly. the solution apparently is to spend even more cash on an arm band. i have tried using it on my other wrist which helps but that means wearing my garmin watch on the other arm which i dont like
the other thing i have noticed is the wide range of data that is recorded for example my Heart Rate Variability has been between 27 and 101, and my resting heart rate 40 to 61. now i had surgery recently and consequently lost some fitness so that may explain the raise in resting heart rate but apparently last night my sleep performance was 98%, pretty good, yet my recovery was only 46%. contrast to Tuesday where i only got 80% of the sleep i needed but my recovery was 95%, and in actual fact i was wrecked all day after a big ride the day before.
ive been thinking about taking it off for a couple of weeks, but i kinda like seeing what it says each morning. i have been disregarding daily activity as i get too many false readings and focusing on recovery, but as already mentioned it seems hit and miss.