I do know that the Katz and most low cost ozonators are
hot spark corona. To my knowledge, only the high end,
medical units like Longevity are cold spark. I don't know
the internals, just what I've read, which is that cold spark
somehow isolates the ozone generation from any heat.
I'm assuming that since ozone disipates more quickly in the presents
of heat, cold spark is more desirable.