Just thought I'd share my experience since I've now used StaminO2 and Ox.
For a month, I did StaminO2 without feeling anything more than a slight increase in endurance. After that, I didn't think it was at all worth the money.
However, a friend told me that Ox was working great for him, so after a week of being off StaminO2, I started Ox. I'm not sure if the overall feeling I got from Ox was part of a cumulative effect of having taken StaminO2 for a month prior (although I had doubted this because I did have a week off), but the difference was very dramatic.
All I can say is that Ox is giving me results similar to the ones Bobo posted, and I plan on sticking with that brand in the future.