there is a guy in Cal. that makes them about 6' long and ports the last two feet. he uses them for pest geese, shoots farther and quieter, and is not a suppressor per ATF. its been in Popular Mechanics and Farm Show. He says its a take off of the Winlite style.
And it's not actually fiberglass, but a very thin steel barrel wrapped in fiberglass thread (something like 10,000 miles or some extreme length of thread).
I think may have been the first shotgun with choke tubes.
Every one I've seen, which isn't many, had a pretty battered looking barrel. They had bumps and gouges and generally looked awful, so I'm guessing they were pretty soft and easy to ding up in the field.