They work great. Nothing wrong with CO2 - fast, lightweight, and inexpensive.

Until they fail. Or you "miss" with your inflation. Or a friend flats and you don't want to give up your 2nd CO2 since it's the start of a really long ride.

I bring a CO2 for racing, but for all my other riding, I use a Cannondale carbon frame pump. Gets to about 95-100 pretty easily, but not much over that.