I'm using an Aqua Medic reactor driven by a small Hagen powerhead at
the moment. Everything is going smoothly but I am curious about
saving some CO2, not for the cost but to space out swapping out the
bottle a little more.

I am trying to get a handle on the efficiencies of those which are
currently available. One offered by Plant Guild, for instance,
promises 100 times more efficiency than passive reactors.

http://www.plantguild.com/power_reactor.asp

Has anyone used several reactors and is in a position to say whether
one is better than the other?