There are also some good points raised in the comments. In particular, I like this comment:

> I’m probably biased because I’ve used Polar for 20 years and Whoop for over 4 years now. I like where Polar has got to on their new Vantage products in terms of activity load, sleep, recovery etc. I started using Whoop because I was frustrated with how far behind the curve that Polar were on the V800 and I liked what Whoop were trying to do.

> Fast forward 4 years and Polar results correlate the closest with how I feel and perform and also with other recovery measurements I use e.g. HRV4Training and Elite HRV. I find Whoop the least reliable in terms of accuracy of data and also correlation with how I actually feel. I like the way Whoop presents data but I have little faith in it due to the accuracy of the sensor etc. YMMV.

That said, I like wearing a mechanical watch, and I'm not a huge fan of wearing a smartwatch, so I'd much rather wear something like the Whoop than a Polar Vantage watch or an Apple Watch. So if someone here wants to defend the Whoop and convince me the data is decent enough, I'd love that :)