I have had a set for years. Neve had an issue with them. I like is they have a little tit on the end, so if the pressure currently in the tire isn't high enough to pop them open you can just pull on the tit to get them to flow
Mine are currently sitting somewhere in the garage. I don't do hard core wheeling anymore and have not used them in at least 3 years. That is also to say I have not run trails hard enough to need airing down in the past 3 years as well. If I can find them I may be interested in selling. But the CO2 bottle I am keeping, I still use that too much.