I have been using a Whoop since March and here is my experience.
Sleep tracking - On the whole, pretty accurate. There have been some nights, usually when I have been disturbed at night, where it has not recorded the whole sleep, but I simply edit the time in the morning when I see the clear discrepancy and it recalculates.
HR tracking - I know a lot of people have had issues here, but I think that is mainly due to where and how the strap is worn. I had a few issues in the first few weeks, but I got advised by Whoop to wear it a little further up the arm and adjust the tightness and since then it has been fine. They even sent me a bicep strap for free when assisting me. I have not used it yet though as I have not had one issue with its accuracy since then. It automatically detects all my workouts, and when I compare them to my HR chest strap data it tracks well, within a few bpm normally. More than adequate for the purpose it serves.
Data - The HRV and RHR data I find very interesting, and pretty accurate on the whole. After a few heavy days working out, I normally start to dip near the red, and after a day or so recovery, I normally am trending to green. What I have found most interesting about the data is the trend over several months. I can clearly see, that on average, my resting HR has lowered over the last 5 months. In addition, my HRV has trended higher on average over the 5 months. I started training again last October but have really been training consistently and with structure since March and these trends validate my increased Aerobic fitness.
The respiratory rate metric they added since covid is also a nice touch, as theoretically if you see a significant change here, it is likely a respiratory issue. The monthly / weekly reports are pretty tidy and smart.
Swim usage - One of the reasons I thought I would try Whoop is you can also use it in water, I don’t swim much, but I have tried it and to be honest it slips on the wrist, so it is not useful for recording HR in the water. Maybe it would be different with the bicep strap, but I have not tried it in the water.
One interesting thing I noted from the data is that it can help you see if you are ill. I had a very minor cough in March (maybe covid…) and my HRV data from those weeks was lower than any other period since I have been wearing it, even when I was not really feeling very ill physically, my body was reacting.
All that said, I am approaching my six months and that is the initial term you are fixed into. I am now considering whether to continue. While I love the data as a data nerd and love seeing my trends etc. I am leaning towards not continuing with it. It does what they claim it does, but I don’t think it justifies the price. There are days it tells me I am less or more recovered, but I generally don’t use this to alter my training plan as I can tell by my training load and how I feel whether I need rest or not. $30 a month is just too much for what it offers. If it were 5 - even 10 I would consider continuing but $30 is just too much, if that is indeed the rate they ask to continue as I think the $30 a month initial period was including a subsidy for the hardware.