They're pretty reliable - however, I consider them to be a one-shot deal - once I crack the cartridge, even if I don't use the whole thing, I don't depend on there being any residual gas left if I have to go back to it at a later time. If I use the cartridge at all, I vent it and dump it when I get home and replace with a new unopened cartridge in the saddlebag. I use a small Lezyne valve head which is very well made, very compact and controllable (tap controls the gas flow so everything doesn't freeze up), and brewers threaded 16g cylinders (come in 10-20-packs from Amazon - way cheaper than bike-specific cartridges). One 16g cartridge easily inflates a 25mm tire to 90-100psi, but I always carry 2 in case I mess up. One time I was in a hurry and didn't ensure that the bead was fully seated all the way around before I inflated, so I had to deflate to seat the tire and use the second cartridge to reinflate. I also carry a very small mini pump to get the tube started prior to installation, and as an absolute last resort if I mess up both cartridges. I only flat 1-2 times/year, so this setup has always been adequate. I'm planning a 150-miler in a month - I'll probably carry two tubes and 3 cartridges.