I think this is where login option comes in, i’ll report back if it works differently between logged in vs logged out.
As for differential - yes it can download incremental given you don’t move the files / folders ( doesn’t have database, but check for file existence in the path )
If one needs a spotify login (and I suppose premium account?) to download in 320kbps, then there really is no reason to not use spotify directly, I suppose.
I am looking for the best way to ditch spotify completely. I need songs in 320kbps though. Maybe torrenting is the way, though it is hard to find songs.