In fairness the canister is just to get a bit of air in to get you to a air hose where you can get the correct pressure in.
I did not use it, as I made my way to a garage, luckily
Top tip. Carry a couple of sets of PVC gloves the throw away type, the wormy thing you thread into the tyre once you have used the reamer tool is sticky, sticky, sticky, the last thing yiu want to do is put that hand inside your glove ha ha.
Oh yeah and if they don't put one in the kit, a sharp blade, to cut the end off that's sticking out of the tyre. Leaving that out could pull the whole thing out ( possibly)
I have used the kit on more than one occasion.