Thanks for the post. I just wanted to point out, though, that the Synergy uses cold corona discharge, similar to the Longevity units. Plasmafire is the only company that I know of that produces cold plasma units.
Also, the construction material used on the ozone path through the machine is also important in certifying that a machine is truly medical grade quality. These 3 brands shouldn't have a problem in this area, but there could be a machine that uses oxygen tanks, but the ozone path does not contain completely ozone resistent material in which case it coultn't be considered medical grade. If the material were not ozone resistent, then it could break down and add something more than merely ozone gas to the equation.