The EnSet systems will run on Co2. I do use this method at shows so I don't have to lug a compressor. However, it will be expensive if you use it in the shop every day and don't use a compressor. I get about 1.5 days off a 5 lb. Co2 bottle with people using it all day at a show. The faster the machine goes the more air (or Co2) it chews through. The input pressure for either into the machine is about 90 psi.
Another thought about using CO2. If someone is considering it they should talk to people who do a lot of paint ball games. I know of a person who does paint ball games for a main hobby. He keeps a large CO2 cylinder at his home to fill the paint ball cylinders. This enables him to keep a ready supply of cylinders for when he wants them. Just a thought.