I wonder why test this on an 11 year old phone?
I have it running on a Pixel 3a and it's definitely smooth, but it still stutters once in a while. It feels slower than Android to me, but not much.
Battery life is indeed excellent, though mine doesnt seem to fast charge.
The camera app was the standout feature to me. The pictures i take look every bit as good as those from Android. I expected the app to be clunky or to have bad colors, but that is not the case at all.
Edit: Pixel 3a not 3
Lineage gives you a decent app ecosystem (F-droid) with the option to set up Play Store for full Android compatibility
Ubuntu Touch has a very limited ecosystem compared to F-droid, but might be enough for someone willing to do most tasks in a browser.
Stuff like phone calls, pictures, sms, podcasts, music, and other simple tasks will work equally well on either OS assuming your device is supported