Syncthing works brilliantly! The web UI is excellent, warns you when you're about to do something ill-advised, and stuff like QR codes makes adding clients and folders fairly easy. The separation between folders and devices is handled well. You can easily have half a dozen shared folders between several computers with any mix-and-match combination including which one is 'authoritative' and so on. I used to use it on…
I would not qualify the web UI of "excellent" : understanding the relations between paired devices, remote devices, folders you want to sync, and so on is harder than what it should be. Likewise, the android application is so bad the best way is to open the web UI on your phone to do stuff (and sometimes, it's the only way to achieve some goals). There is definitely a lot of room for improvement for easier adoption,…
The second thing I like is that it is a successful FOSS project, meaning it works and is being regularly and often improved by its users.
Your comment, as helpful as you may feel it is, is contradictory to my second - very strong - feeling.
I really think to UI works quite good, and by god, if a better solution is so obvious to you, why haven't you proposed it yet, or - god forbid - made a merge/pull request??