V4.xx is now not only very capable (which it was from the start), but also very stable. Sync profiles are also easier to manage.
Due to some stability issues and Unicode compatibility issues with SFFS, I went back to hand-made BC (Beyond Compare) scripts and batch files for scheduled sync'ing when BC3 was released. Relying on a 3rd-party scheduler (BC3 doesn't have one) and various scripts and batches (for BC3 scripting isn't capable enough) nevertheless made maintaining several sync/backup jobs difficult. So I tried SFFS again recently (about two weeks ago), and haven't had any issues so far. Its rock solid now, running non-stop on my system.
I still prefer BC3 for manual operation, and its Linux ver. is just as useful. The interface is perfect for me, and the ability to align differently-named folders/files is a godsend. For scheduled sync/backups, however, SFFS is the better choice.