CO2 powered guns have a bit more recoil and can usually be found easier in “big box” stores.  Green gas mags are quicker and easier to fill, and green gas is cheaper in the long run, and are easily found online at stores like Amazon. Per Cartridge of CO2 you can get up to 100 shots per magazine. Per magazine fill of Green Gas you can get up to 130 shots per proper magazine fill, each can of green gas will provide up to 2500 shots depending on firing rate.