Question: Anyone have measurable experience with Brownell's retro carbine barrels?

Background: I've been wanting to buy or build a simple and very light, fixed carry-handle, carbine-gas upper w/ 14.5" barrel (something very much like an RO723) - it will go on an NFA lower. I require quality components as I intend to put some use on it. I probably won't need to save my life with it, but you never know. At any rate, a suitable barrel has been been quite elusive.

I would prefer Colt and the easy way is probably a new M4/6921 barrel, but I really want the lightweight profile (a little nostalgic perhaps). I've considered having a 6520 barrel cut down, but . . . at this point, I am considering other options as well. I have had good experiences with Brownells - LOTS of parts, very long time.

I will appreciate hearing feedback on these barrels from anyone with some experience to share.