Man, I would be scared to be in the same room as that thing. But to be fair I hate bristle worms the same. Worms in general freak me outThose are really rare, is the thing. They're scary, but they're rare. And at least they don't spread all over the place like aiptasia or red bugs. There are many species of eunicid worm, but only a few that get big, and only a couple that get huge like those.
Personally, I think they're really cool. I'd love one in a species tank. 10g, maybe some invasive corals, and teach it to come out and eat from a set of tongs. Wouldn't be hard.
I saw a picture once of this really neat black-and-white striped one. Someone had brought it into my LFS to show them and get a big breeder box for it to live in. That one was maybe 6"? And I don't think it was the same species as these really huge ones.