I use both CO2 and beergas, the beergas for my stout tap. I have tried two types of beergas, much prefer the 75%N2/25%CO2 'Guiness' mixture for the stout tap as it does not over carb the beer. 40%N2/60% CO2 resulted in overcarbed beer for me regardless of pressure I set. The bottle connections are different and are not interchangeable. I only use the mixed gas for the stout tap, if I only had one bottle it would be CO2.