I was a recent convert to CO2 'thingy' (glad I'm not the only one that calls it this!), used it once and was impressed by the simplicity and speed of it. Went to the LBS to buy a replacement CO2 cartridge, didn't know there were different size cartridges available so not having my gizmo with me figured "bigger is better" and bought the largest one. A few days later I got around to actually checking if the cartridge was the right one and found to my dismay that it wasn't. Back to the shop I go to exchange it. Guy at the shop wouldn't hear of an exchange because I no longer had my receipt. No amount of reasoning was going to change his mind. There is another bike shop just around the corner so I went around there to buy one rather than the original shop (it's a principal thing, if I get bad service I walk) but they didn't have any. I was planning on going on a long ride the next day so I needed a cartridge so I was forced to eat hunble pie and go back to the original shop again and buy some. I bought two, took them home and fitted one to my gizmo and figured everything was sweet. THis was a few weeks ago, been for several rides since then, several hundred kms puncture free in fact. Then I was about 20kms into a 100km ride and I got a puncture. So I pulled off to the side of the road and started to pull the bike apart and replace the tube and reinflate the tyre using the CO2 'thingy'. Problem is it didn't work. The cartridge still seems to be wrong, or there is something missing off the trigger device 'cause it won't puncture the cartridge. By this time 22 of the 23 riders I was with had already ridden past, luckily the last guy stopped and asked if I needed a hand otherwise I'd probably still be out there! He had a pump so we resorted to old fashioned muscle power to reinflate the tyre and I was on my way. I think I will reinvest in a pump, the money I've (mis)spent on CO2 cartridges and the trigger gizmo I could of bought a good one. Oh well, you live and learn!