In my experience, syncthing works as advertised, however the UI is a bit of a mess(as many open source projects have).
Especially the android app. The status of what the program is doing at the moment is not communicated very well. The refresh rate for status updates seems to be very low, and so you have connection status being disconnected, then jumps to connected after a few seconds of frustration("why isn't it connecting!!"). Then it sits there at 0% ("whats wrong!), and jumps to 64% after a few seconds, then 99%. Then sits there("is something wrong?"). Eventually it finishes and everything is fine("yay it worked!").
Love the project. Hope they get UI experience down though, as it is the main thing holding it back in my opinion.