Is this thing good or bad(pic)

[Burrito]

I was trimming cheato and saw this. Put him back or garbage

 

[KJ]

Harmless Bristleworm good CUC,

 

[DarkSky]

Harmless Bristleworm good CUC,

Harmless to your reef, just don't touch them unless you want tiny little bristles in your skin. :)

Ouch!

 

[BellaCoop]

+1 on Bristleworm! If you put a light on your tank a little after lights off you will probably see more. I use to take them out but now i keep them in.

 

[justmee]

If it was me, I would trash it... I hate bristle worms with a passion, those thing could multiply quickly...

 

[BellaCoop]

Ad well +1 with @justmee its best to keep an eye on them.

 

[HawaiianReef]

They are a love-hate hitch hiker in reefing.
Good, because they control nutrients by turning over your substrate, eating anything they can find in there.
Bad, because they populate like aptasia, maybe worse. Once in the substrate DON'T ever stick your bare hands through it. You wont feel it then, but days later you'll get little rash like bumps that itch until you finally cut them open and get the bristle out of your skin. This can flare up months later as well.
Also Bad, they populate ANY where they can. So rock work will be full of them. If you like fish that hide in rocks, like goby and blennies, your buddies are going to be irritated by the bristles as well. Often forced out of their hole to pull out the bristles with their mouths... all day and night.

The only argument I hear about these pests, is they are a great CUC.
But there is a plethora of great CUC without the negatives that bristle worms have.
I would prefer them anyday