It has not been a problem in my experience. There isn't major development (proper support for inotify and flexible topology would be nice), but Unison does what it says extremely solidly. There's certainly an active user community and the occasional bugfix/feature. Reread that notice again concentrating on the good parts, and take a look at the changelog. There's certainly activity, it's just not time intensive - this is both the blessing and apparent curse of using a high level language.