1. yes it is compressed air
2. where would you be getting it filled (paintball site , dive shop , somewhere else)?
3. even though they all do the same job so many differant places use differant fill rigs (they all fit standard bottles).
the site i work at uses a fast fill rig which has a big air bottle with twisty knob and purge lever
the site i train at has a slow fill system which is a small twisty nob and you pull the knob out to purge it
and tournys i go to have a inbetweenish speed fill rig with just a handle you push down and it fills when you let go ofhandle it purges automatically.
one thing im going to say if you ever use a fast fill rig be VERY carefull
i had hose ping off and smack me in the face repeatedly abou 10 times ripping my cheek open before i had even realised what had happened.
i personally think the set up is realy bad.
4. one more thing abut bottles make sure yours is in test if its not you wont be allowed to ue it (no proof that it wont go boom)
there you go i think that should be about right feel free to correct me if im wrong about anything
p.s i know inbetweenish isnt a word but i thought it sounds cool