Its often asked if CO2 canisters are allowed on planes and mostly a lot of conflicting information is given in the answers. I recently found the definitive answer so will share it here.
At the time of writing CO2 canisters (max 4 x 28g/50ml per person) are allowed on planes, both in cabin or hold baggage, but prior approval should be sought from the airline and they should be declared at check-in.