it's been said elsewhere-- but you should get a pump... youwill run out of CO2 if you have a slow leak that needs constant filling, and the 'reuse' feature doesn't always work... If you are in a race (triathlon for example) where you have to do your own repairs and time is an issue, CO2 works great. Any other time, a pump is your friend. It never runs out of air. There are frame pumps that fit nicely into any bike frame or mini pumps (I hate these-- you need about 150 pumps to get a tire full) that fit on your water bottle cage or in your pocket.
train safe-