I had tried both and they treated extensions as the rule and would refuse to upload a tarball since it couldn't figure out where to put it. I'm also pretty picky about my music layout and I couldn't see a way to upload a directory structure, just files which presumably get "auto sorted" (poorly). That was when it didn't time out or crash of course.
It put the (mp3/flac) files where I told it to, rather than sorting them into random subdirectories according to its own scheme, and the performance was reasonable. However, it may be a bit unstable yet; it seemed to lock up at one point while I was scanning through the camera folder with Gwenview, requiring a USB reconnect.