I'm using an iPhone SE (original) for work/normal use. I charged the phone up to 100% and unplugged it, this morning (about 6:55 AM). Had to make a lot of phone calls and reading/sending some mail with Outlook thorough the day. Right now (11:37 PM), the phone is sitting at 79% battery left and hasn't charged ever since then. For me, battery life is great.
I have to say that performance has improved, compared to iOS 13.7. Scrolling animations are a bit smoother for me and apps seem to open faster. Unlock animations are the same for me. TouchID, however, seems to work slightly faster.
The only issue I've seen on this phone is keyboard lagging in the notes app. In WhatsApp, Outlook and Evernote: I have no issues.
The battery on my phone is about 4,5 years old and is sitting on 87% max capacity