I can't speak to using DOM tubing for barrels as I haven't looked into it any further than this thread. I've never seen the reason to use them or been offered one that I know of. As far as cutting corners for profit....there are people like that all over unfortunately.
As long as I have been hanging aroud this ml game, I had never heard of DOM tubing barrels until I ordered my Jackie Brown fowler. Since then I have gotten an earful.
Can't say that I am thrilled with the idea. But, I didn't panic and still don't. There are several builders who use DOM and, thus far, I have not seen or heard of any reports of failure with these barrels.
I do know a few things. In industry there are applications where extremly high pressures are generated and put through pipes or tubing. Failures cannot be tolerated. Being a piece of tubing is not a condemnation, safety wise.
There are some who claim Douglas barrels are not safe because they are made with a certain type of steel. To which I respond: :blah: There are gazzilions of them in use, safely.