Desktop runs great, but Firefox on Android seems to be noticeably buggy here and there sadly. I still use it, but I can imagine that might drive people out of the ecosystem.
Many people get used to the synchronization of their passwords / bookmarks cross-channel. More advanced users have a separate password management for this I'd figure, but that's not the default for 90% I'd guess.
Well, it depends on your bubble I guess. But personally I'd say it's underrated and overrated at the same time, but mostly underrated.
It depends on your expectations and way of usage in your toolbox I'd say. It keeps surprising me weekly how fast progress is. But we get used to it perhaps.