As far as I can tell, imageoptim eats this project's lunch. The examples given on optimage's own benchmark page show imageoptim clocking in at around half the total filesize of optimage for the entire benchmark.
Even in the specific examples that are supposed to count against imageoptim -- the destructive chroma sampling, the 'broken gradient' (I can't see it), the orange sneakers (imageoptim's looks better and not overblown colors), or the rotated beach scene -- imageoptim is dramatically smaller on all of them. It puts up a 76k file vs 141k, a 5k vs 14k, a 72k vs 177k, and a 750k vs 1340k.
Halving the filesize for such small differences is exactly what I want in an optimizer.
My biggest complaint with imageoptim is that it's primarily a mac tool, with only a secondary online interface for the windows/linux crowd. But then this project has exactly the same flaw, so there's no gain there either.