I'm unclear why release version 1.8.4 is Tiger-only, but 1.8.4b is Leopard-compatible.

Great utility. I've successfully used some of the same options that some others here are having trouble with, so it's possible that some of the trouble some people are seeing, might be due to other problems, like directory damage, bad blocks, System software damage, etc., and that running the same options in any utility, or from Terminal, may just "manifest" these problems too. It's also possible there are sometimes problems in OnyX, particularly the betas.