I've been a paying user for years. Their desktop UI is awful. They introduced a feature that took me hours and hours to disable (the file not downloaded until you try to open it thing). One bit of documentation pretty much lied about turning it off. Turned out it had to be disabled in more than one place.

I still use them as I don't have time to move else where. Plus they run on Linux and windows which is what I need.

I wish they had "I'm only interested in file sync" mode so that the whole mess of other features is hidden from me.