I consider my 19cf pony to be the minimum I'd want for the diving I do. I'd be stretching the envelope with a 13cf, and on a 100fsw dive, I'd consider the envelope broken. The H2Odyssey only gives you 6cf -- I'd consider my safety envelope thoroughly shredded with that. (If I were only diving in 33fsw sand-bottomed desolate wastelands, it may well be plenty, but my envelope has to fit more than that.)
That said, the true measure of the H2Odyssey in my mind is that they have a new 4cf version!
(I'm just waiting for someone to come out with one that's just a big lift bag. You attach it to your BC, and in an emergency, you pull a string and it blows a big "air bag" around your head to let you breathe as you rocket toward the surface. They could make it 100% O2, too, and market it as "Gets you to the surface and starts your DCS treatment, all in one tiny package!")