i have just got my self one of these (link at bottom of post), instead of having a BIG hpa bottle hanging off the back of my Tippman A5, i have put it in the back of my battle vest.
i find it useful because it makes my marker seem smaller because i don't have the bottle getting in the way... my friend is looking into a remote line that allows him to hook up 2 pistols (Tipx) on to one hpa bottle. depending on what you play is how useful it will be. if it was me, i would play plenty of games with your chosen marker and bottle size before getting a remote line. but thats just me.