You're right, there are many alternatives but the ability of sharing for free if you use peer to peer only and the possibility of using folders with their original structure seem nice (if they work!)
SugarSync can sync any folder on your machine, preserving file structure. However, their sync to Android local storage(the main reason I signed up) is a bit buggy, so Cubby may be a decent alternative. Agreed that free P2P transfer is potentially quite interesting.