iPhone SE (DD) here.
So, I only got on board with iOS 12 beta with Public Beta 8, and, while it seemed slightly faster/more responsive, it wasn't a big deal.
Beta 9 is as if they added the code to speed things up, as if it wasn't there before, I mean, everything is noticeably faster and smoother.
Apps load much faster, it acts more like my iPhone 7 did than an SE!😀 ...I only have one app not working, and it's an inconsequential app. If I had app issues I might have gone back to iOS 11.
Only issue so far, voice memos disappeared, which is fine, they are backed up in iTunes, I don't need to keep them all in my phone, in fact, I didn't realize how much space they took up, so, I have lots more free space in my iPhone. (Mentioning this so ppl know to backup before updating)