Well, my barrel arrived. Service and shipping was very fast, shipping was $7.95.
Markings: C MP 5.56 NATO 1/7 HBAR. Barrel appears to be new and unissued, with a few light scuff marks from storage. Chrome-lined from chamber to muzzle, wrapper date is 6/91. No FSB as advertised, and an unexpected bonus for me was finding that no FSB holes were ever drilled in these barrels. Nice! I assumed that they once had FSBs installed but were removed for some reason - I was wrong.
Lack of a FSB and barrel nut may be a problem for some people, but if you're building a floated, scoped rifle these barrels are a great choice. You know you were going to float your barrel and stick a flip-up front sight on it anyway.
I have absolutely no need for any more of these but this barrel is so nice I have the urge to buy more.