Anecdotally my Garmin's stress monitor seems to just be a hangover monitor.

a study has concluded that smartwatches cannot accurately measure your stress levels – and may think you are overworked when really you are just excited.

Interesting. I was wearing a Garmin watch for a couple of months and got a notification about high stress levels once. I was sitting at a table with friends, drinking beer and talking. I wasn't stressed at all (maybe my body was stressed due to alcohol consumption though). I remember being amused by the notification, but wrote it off as some kind of measurement error. Apparently I was just excited :)

I like some of the stats like sleep and steps and obviously seeing the time, but I'm not at all interested until there's one where it's all on watch with really good battery life, or the companion app doesn't require an account or sending data to the internet. It's not necessary unless they want to collect your info. And that's too much personal info.