FOSS apps often suffer from mediocre UX/UI since the expected audience are power users, but it alienates users that aren't. They're functional for those who need it, yes, but is the GUI high quality? More often than not, they aren't.

I'm not saying FOSS can't have bad UI, like Blender for example, but those are the exception, not the rule.

For me, Connect and Thunder are getting there, but they don't have the same level of quality and finesse as Sync. Though to be fair, Sync has a decade of work put into it.