Ions can run on CO2 with proper anti-siphon, but compressed air is a much better option. But the most important question is: what is available gas-wise wherever you'll be using it? If you can't fill the bottle you've bought, then it won't be any use to you.
Most punter sites used to run all their site guns on CO2 but many are switching to air now; on the other hand, CO2 is often not available at tournaments any more. This shift is because air bottles have become much cheaper over the last 3-4 years so now it's not much more expensive to use air, which is much kinder to your marker and runs more consistently. Not so many years ago a compressed air system would cost you about £350, so only tourney players would look at them. Nowadays preset air systems are so much cheaper, so CO2 is dying out.