Personally, I feel that carrying two CO2 cartridges is better than a mini pump.

The cartridges are much faster to fill the tire – and obviously take much less effort.

If you're having problems using the CO2 correctly, it's best to practice. They're super-cheap, so going through 2 or 3 of them in the interest of proficiency won't break the bank.

In fact, regular practicing of tube replacement / repair is a smart idea, because you'll be prepared and efficient for when it happens in the wild. Technique is the difference between a 5min stop and a 20min stop.

Some people like the security of a mini pump for worst case scenarios... But I think it's unnecessary with 2 cartridges.

I mean, maybe if you're riding 100+ miles solo? But for most, that's rare I would think.