I use whoop and have had it for 8 months, so I tend to trust it for my sleep stats and HRV. It is an ongoing cost, however, so I think it is out of reach for many, even if you sign up longer geem to get a cheaper per month price.
I am happy with my Garmin VivoActive 4s. Have used it only 3 months. I originally picked it for continuous, all-day spo2 readings and step tracking. Its sleep stats are not as precise as whoop's but it does have that Body Battery measurement, which I feel helps to quantify my strain easier than whoop's 0-20 "strain" score (based on Perceived Level of Exertion).
Because I am taking a beta blocker, whoop is less likely to register a strain because its algorithm seems to be influenced by your max heart rate for that time period. This is fine for non-ME/CFS people. Because I am pacing and taking beta blockers, it rarely registers anymore strain. If I were to eventually not need beta blocker, then I would be more trusting of the strain scores.
When my whoop membership runs out, I will be sad to take off the strap because: it is so comfortable to wear (cloth/nylon and old style snap closure wristband), is so easy to charge (you never have to take it off and so, never lose datapoints), waterproof, collects data multiple times per minute ( I forget how many...250?), great sleep stats, can broadcast HR via BLE and whoop API allows for fetching the data through 3rd party util habitdash.com).
But, in the end, economy wins out and I feel the Garmin VivoActive that I have does the trick. I don't like the plasticky strap and have not been successful in replacing the strap style to one similar to whoop's. The graduations in the strap never quite match my small wrist and tends to make me itchy sometimes.
