Yeah everything I know about them, I learned from Doug.

Rather than re-typing everything you need to know, I hope it's OK to send you off to a different forum, namely the framebuilder subforum on Velocipede. There's a years-long (I think) thread there that might take a long time to read, but you'll be well-versed by the end.

I now have two of them. (I had 3 but sold one!) One is a 5 liter per minute (l/m) unit and the other 10 l/m. The 10 l/m units are far less common; you'll find a hundred fives before you stumble on a ten on Craigslist. The reason I keep both is to run two torches, one of them a rosebud for quickly heating up something heavy. Then when I'm at brazing temperature, I hang the rosebud on a gasaver, a switch that turns the torch off when you hang it up. This is an extreme luxury for a home-gamer. No one needs that! But I got spoiled by having that setup, one place I worked. I got almost all my stuff dirt-cheap (mostly CL), but even if free, two O2 concentrators take up a lot of space in the shop, so believe me I am not recommending that.

BTW, to OP or anyone else reading this, if you're near Denver, I might have a lead on some reasonably-priced used ones. A guy on another forum (the framebuilders googlegroup) mentioned that he bought one from a guy that had a couple dozen for sale. Not rebuilt, just used. He charged $250 for a 5 l/m Devilbiss, but he also said he'd stand behind it, and replace it with another one if it didn't work. Lemme know if interested and I'll put you in contact with the guy who posted that.