I have read about it a bit, so I think, I can tell about cons and pros of holding the bristle worms in the fish tank. Actually, I want to begin with cons, because, as for me, there is only one significant con, that I have seen, and it's their "beauty", that can make afraid for children. That's all about cons. Indeed, there are a lot of pros, I have read about: begining with their "cleaning" of the aquarium, I mean, they eat only detritus and ending with the fact that they're growing fast. I have read about these fireworms at https://arcreef.com/bristle-worms/bristle-worms-fireworms/ and advise you to do the same and make your own conlusion, thereby answering at your question.
Frankly speaking, bristle worms can be found in salt water aquariums and there are mixed claims about them. Some people claim they are good for the aquarium ecosystem because they tend to eat food that fish leave behind and they clean the aquarium just like an algae-eater, but some people consider them to be pests that need to be eliminated.
In Latin, this creature can be called “hairy worm” because the word Polychaete actually means “many hairs” and by the looks of the creatures there is no objection why the people who first discovered it settled on that name.