I wouldn't recommend taking solely a CO2 inflater, I've been out cycling when a friend's bike had a puncture. The only inflater he had was CO2 and it decided to pack up at that point, fortunately I was carrying both but I wouldn't suggest using it on it's own.
A CO2 inflater is good to get you to the next bicycle shop, however multiple cartridges are a pain to carry and if you run out then you are going to be having a long walk.