Not a bad idea !
Take one of these and after a few trip you’ll save a few quid 
I decided to roll the dice on my flight back from Hamburg, and put 2x CO2 in my toilet bag (hold bag). It came through the other end without any issue (Eurowings).
Just thought I’d add to this. Flew with 2 in my bike case last week. No issues. Baggage handler at Bristol asked if I had CO2 in there, I said yes and off my case went. No questions asked going out of Girona.