I have used Nextcloud for about two years and really like it as well; the only problem I have encountered is that the client sometimes slows down my OS X machine and it's not clear how to proceed in debugging the client.
Sadly it's still in testing, but we (finally) managed to hire a 2nd developer so we're moving forward... 3rd job position is still open so if you're in C++ or know somebody who is - let them mail us!