For those who have a device - do you have to tell it what you are doing ?
Ie if going to gym - do have to load a gym workout ? - or does it automatically know by increased exertion, HR etc ?
I use a Whoop and also an Apple Watch*. Both are linked so I only tell the watch what I'm about to do.
Both devices are capable of inferring what I'm up to and are usually pretty spot-on if I didn't tell them but my preferred watch face has a complication for activities so it's just two touches to tell it I'm about to start a ride or a walk etc. Whoop then picks that info up.
Given the size of the user base and the development resources available, I think the Apple Watch will develop into a very sophisticated health & fitness monitor that could eclipse every other similar device. The upcoming changes in WatchOS9 alone are quite significant without any hardware changes.
Whoop will also detect sleep but I turn my iPhone's focus to 'Sleep' when I turn-in and that info gets pushed to the Whoop.
Whoop's HRV info is limited to your sleep as far as I can tell and it's used specifically for calculating recovery. I assume it can measure outside of this and their servers may well store that but I can't see any use in that data for my own use case. HRV on the Apple Watch seems to jump all over the place and I've not been able to make any sense of it.
Apple Watch/Health app also comes-up with a cardio fitness/VO2 max assessment which seems pretty good as a trend if not an actual score. This is limited to walk/run and doesn't show anything for cycle rides.
Regarding the Garmin 'Recovery Time' - it seems to be based on a brief snapshot of how quickly one's HR is dropping and is a total gimmick.
* I bought the Apple Watch as I'm a total Apple fanboy and the Watch7 finally ticked the boxes required for me to get one. I bought the Whoop as I was preparing myself for a fitness drive prior to prostate surgery and to augment my post-op recovery. I bought it on a 24 month sub which makes it £20/month and there was a 30-day return policy so I could decide if it really was for me. The money I've saved by quitting booze as part of the fitness drive has already paid for the Whoop subscription!