Keep in mind, if you get some fancy whiz bang cylinder, you may not get it filled very fast, you may have ot send it off and get it filled and get it back all scratched up several days later. Its the main reason I just ended up with a 20 CF steel cylinder. Still plenty portable. You may be able to find a place that will fill it on the spot, but I would find that out before you buy it, it's a lot easier to just exchange it.
