@alextecplayz here's the help page, so you can judge for yourself https://support.mozilla.org/en-US/kb/firefox-ai-controls. We mostly refrain from using "opt-in" because people have different definitions of opt-in, e.g. some have said it's only opt-in if it's in a separate binary.
I asked for UI that shows downloaded models, but there wasn't time for that in 148. I'll keep asking for it 😀