Yes, installed smoothly, seems faster. For example, time until the camera is up by swiping right on the lock screen is 2-3 seconds instead of roughly 6-8 seconds.

Same here. Installed it on 5s, seems faster (not 100% sure though, maybe that's a placebo efect) than iOS 11. Definitely does not feel slower, so it's safe to install IMO.

I went from 10.3.3 to 12 directly. There doesn't seem to be any performance degradation.