the problem with CO2 is the way the cartridge is held in the mag: if the mag uses a screw system that tightens using an Hex key, it's probably going to degrade and the hex key will progressively have trouble sealing the cartridge in until the point where the hex key doesn't work anymore at all.
I've had the problem with my KJW hi capa.
Look for systems that will be easy to tighten completely even after some intense use.
for instance in this type of magazine the hex shape will be destroyed quickly so you'll have to rely on the big fence for screw drivers.
the big fence sucks with regular-sized screwdrivers and you'll need a giant one.A coin doesn't work for tightening the screw enough.For that reason I went back to propane after a few years with co2.