If you are looking at flights for a paintball tournament, you should rule out Easyjet. You cannot put your marker or barrels in your luggage at all. We had to post out our guns and barrels when we went to Sweden with them.
However bottles they didn't care about it would seem.
And having an on/off on your bottle and open will probably not suffice should they want to look inside your bottle. It isn't the pressure they are bothered about (plenty of people have flown with full bottles after forgetting to empty them), its the drugs you can stick inside them and wont be detected on a scan.
So try your absolute best to get the reg and bottle apart, if it just isn't budging, get one off somebody else to be sure.
I'd possibly be interested if it turned out quite cheap, but really should save some money for Spring break in Miami
