I crush the canisters all the time to save room.  They are easy enough to pierce with a P38 or the can opener on your Swiss Army knife - just pierce the side, not the bottom, as if you were opening a can.  Once out of fuel, there is no pressure left.  I take a narrow rock and dent all around the circumference, which provides the relief to allow the crush to start, then drop a heavy rock on it several times.  Really quite easy.

I use about 4 230 gram canisters on a 10 day for 4 people with the way I cook, with my MRS WindPro.  Coffee/tea every morning, about half cooked breakfasts, no cook lunches and all cook dinners.  I'll use one more if we're catching a lot of waldos.

pd