What is this? Should i keep it outta my tank? or beneficial?

[Noslen34]

I just picked up some chaeto, but i found 3 of these guys in the bag, what is he? Would it benefit my tank or is he a pest? Should i put the chaeto in my sump?

Thanks

 

[Noslen34]

Here's another picture.

 

[SushiGirl]

Beneficial amphipods.

 

[Noslen34]

Beneficial amphipods.

THanks!