I relied totally on CO2 for years with my road bikes. One 16 gram cartridge was perfect for reinflating a 700 X 23c road tire. Never had a misadventure.

After I switched to recumbents, the first flat that I had was at the front of our Screamer tandem. A 16 gram CO2 left the 20 X 1.5 tire pretty soft. I doubt it even had 45 PSI in it. I use a Topeak pump now.

Years ago I had a bike shop lady tell me how to pick out a pump. "You don't have a flat very often but, when you do, you're likely to be aggravated."
"If you're the kind of person who doesn't upset easily, it doesn't matter because you don't flat very often. You can get the smallest most compact pump you can find. It will just take longer."
"If you're prone to anger, you want the biggest, fastest, most convenient pump you can handle on your bike."