RM,
Also a VA care recipient. Don't bother with a concentrator, they can't deliver the high volume O2 that's needed to abort CH attacks. The VA provides me with an unlimited supply of "E" tanks. They're easy to store and transport. You can buy your own high flow regulator (the max they would provide me was 15lpm). I've bought my own 25lpm regulators a long time back. You can start huffing at 25 then turn it down as the pain eases.
Myself and many others have tried the concentrators, and they're simply useless, due to the low flow.
Cheers,
J