Are you in the U.S. ?. Is so and if the "bottle" is over 2" outer dia., yes it (by law) requires testing. I don't know what FX is using but it better have the "DOT" makings or you'll not be able to get it tested ( thinking some evanix rig's do NOT have such making so can NOT be tested).
Now maybe the TSA stop's you on the Highway, see's said HPA bottle, notices it is out of date, and ?????????????????????????
But, real world, safety is up to you. Hopefully people will do the right thing and observe proper testing.
Under 2" outer dia. and it's up to you to decide what is safe.
John