I just got this on my Nokia G50 and it's an Android One device so a stock experience. One thing I noticed is the massive rounded tile dialogues and wallpaper colour matched theming. Performance wise it seems no different as of yet and as far as I can tell no functionality broke.
I'm not sure I like the rounded UI stuff but the large clock on the lock screen is fairly cool. What's the UI 4 experience like? Any quirks to look out for when my Tab A7 eventually gets it?