Sc is very, very cool but you must sync both ways every time, so after some time, if your phone runs out of space, things get hard. The "do not erase on 'server'" setting is pretty well hidden and claimed not to be supported and can break things.

Also, for "one way sync", with super easy setup, i have not found an alternative for btsync (now called resilio). SC is too clunky to set up the client and in this case, running Nextcloud server + setting up clients is crazy complex. TIL about Unison and will try it out...