Is this worm/millipede thing good or bad?

I've had my tank set up since this last December (almost 4 months) and this is the first time I've seen this worm. Is it one of those deleterious flatworms that I've been hearing about or something less dastardly. Any help would be greatly appreciated

 

Look like a bristle worm/fire worm, a good guy, nice part of a clean up crew. Just avoid touching him.

 

They sometimes attack fish if they get big, you will get a rash if you touch it.

 

Good cleaners. That's about all that's good. They keep ammonia and nitrate low, but don't help with looks.

Bad: they get pretty large, have stinging bristles, and attack cuc or fish when large and underfed.

 

Here is an informative link regarding their care and behaviors.

Short Take: Fireworm Husbandry?! — Advanced Aquarist's Online Magazine