Propane gives you slightly less cooling effect and oomph than the n2o but as Kenny said, it is a fuel. It has an octane rating of somewhere in the 118 range IIRC. Of course, you're not using that much if you're spraying propane but still, every little bit helps. It's cheap and you can get it almost anywhere. You have to have a bottle setup though where you can extract it from the bottom and not the top so that it is in liquid form in your lines. I looked into it a few years ago as a small shot to spray on top of my blower, mostly for the cooling effect. I never got around to doing it but overall, I think it would have more pros than cons.