There is a bit of technique involved with using the CO2 cartridges. I saw one used on a group ride and got the idea. The next time I had a flat, I used one. It was far simpler and easier than I envisioned.
1. Remove old tube & replace with new tube.
2. Screw the adapter onto the cartridge. This will crack the seal, but as long as you leave it fully screwed on, the CO2 will not come out.
3. Put the head of the adapter on the tire valve and unscrew the cartridge just a bit; you will hear the air going into the tire. After just a bit, screw the cartridge back in to stop the flow.
4. Make sure the tire and tube are properly seated.
5. Repeat step 3, going a bit at a time, and check how hard the tire is in between each "shot". Compare to the other tire on the bike to get a sense of how full is full.
I think the problem a lot of people have is they assume once the CO2 starts to come out, that's it, it all comes out. But you can modulate the flow, even with the cheapie screw-on adapters. It's a lot more controllable than I thought.
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I stop for people / whose right of way I honor / but not for no one.
Originally Posted by
bragi 
"However, it's never a good idea to overgeneralize."