Unison is beautiful, as it has a formal specification with proofs of correctness for its bidirectional syncing. Bi-directional syncing is hard to get right and many devs have been subsequently shown to not understand the problem fully, for example DropBox: https://www.cis.upenn.edu/~bcpierce/papers/mysteriesofdropbo...

My instinctive reaction is not to trust any brand new effort without more evidence of its correctness.