I made the same experiences. BTSync basically killed my Raspberry Pi 3 times by using 99% CPU, forcing me to hard reboot. The mobile App was really cool, but recently it's just buggy and neither download nor upload work anymore (On iOS as well as on Android). A while ago, even the desktop app became unreliable, causing me to ditch BTSync altogether. I'm currently using Owncloud 7 and I'm very happy with it (File sync in Version 5 was unusably slow for me), however I'm keeping an eye on Syncthing/Pulse as I prefer decentralized solutions.