I still have yet to find a bristle worm in my tank that is beneficial. At the very least, in my own experience, 9 times out of 10, bristles are bad. I just don't want them in my tank. The single fact alone that they have the ability to grow to over 4-6 feet and eat corals/fish is enough for me not to have one in my tank. That freedom to grow is something I'd need to constantly monitor, and I'd rather just spare myself the worry.
Bristle worms have toxins in their bristles, and although they're practically harmless when they're this small, that doesn't change the fact that they also have that potential to sting.
I just wouldn't keep them in there. JMO.