It is a ghost shrimp. It is not bad at all. Feed him flake or tiny bits of whatever you feed the other critters. He will mostly just sift through the sand to get his dinner, cleaning up waste.
Some have been known to pair with gobbies, though that guy looks tiny. You won't see him much, other than the occassional spotting as he dumptrucks little mounds of sand out of his burrow.
Good addition to a reef.
-Ron
PS:I'm no expert, but iI looked into having one last year, still may, since my pistol shrimp may have died, and my goby is lonely.