I ordered one, just to try it. I had those that you add pressure while closing it but it's heavy and because of the material used cracks easily.
I'm more interested on a device that can add/keep the ball pressure at higher quantities to be used with my ball machine. $200+ sounds kind of expensive for a simple piece of plastic made by the company (I can't remember the name).
People post here that you can make one of paint barrel (or similar) but I do find those posts useless when there is no link on "How To" actually do them. Maybe just a simple list of all the components needed with links would be really useful for most of us.