My mini CO2 inflator gadget arrived today, it is really tiny
...
I've resisted the urge to try it out and waste a cannister. From the instructions it looks completely fool proof. The big question is how many cannisters should I pack on a 300, 300 and 600? I don't think I will risk going pumpless.
That looks like the same one I've got.
I normally carry a pump, because it's useful for doing things like putting a bit of air into the tube before you try and get it into position inside the tyre. This may be possible with the inflator, but my suspicion is that it squirts the CO
2 in too fast, and I'd risk bursting the inner tube!
I've yet to use more than one CO
2 cartridge on a ride, but I normally carry three. That's partly because I have two of the rubber surrounds (to stop your hand freezing in use), so I sandwich a third cartridge between the two wrapped ones, and they won't clink against each other in the bag!
Before I had an inflator myself, I carried one on the first Martletts ride last year, which was Simon Legg's, and about a dozen cartridges (and 25g cartridges, which are stupidly expensive compared to 16g ones). We used three or four on that ride, but that was 120 or so people, many with randomly maintained bicycles.