I used to own a Whoop and an Apple Watch with the Auto Sleep app, and I now wear a Fenix 6. I never notice the Fenix (it just replaces my other watches) other than when trying to wear a dress shirt (sleeves don’t fit over it). It’s more accurate at tracking my sleep than my Whoop band was and it’s uncanny how well it notices the moment you fall asleep. The Whoop was also too large to fit under a shirt sleeve and for me personally was not comfortable or accurate at tracking HR. The Apple Watch with the Auto Sleep app was just as accurate as the Fenix and Whoop, but I didn’t like having to charge it daily, and I cracked the screen. The Fenix also provides lots of other functionality that I use so I’ve stuck with it. I’m not sure I fully trust the “sleep cycle” data on any of these (how much was REM vs light vs deep).
As others have mentioned, ALL sleep trackers are only accurate to a point, and will do things like not notice naps, not track activities very accurately, or tell you you’re well rested when you feel exhausted or vice versa. My recommendation is to just buy the device that meets your lifestyle preference (ring, watch, or band) and accept that there will be days when you agree with it and days when you don’t. If I owned and loved an Apple Watch and didn’t mind charging it during the day, I would just stick to using it with the app.