A few of the backgrounds just seem to be either useless or just odd. For instance, why is it that an Arbiter is better at chipping away cover then a guardsman? I never knew they spent so much time practicing shooting walls.
The Arbiter should get unique use from something like intimidation, interrogation, or even investigation. Maybe something like brute force interrogation, to allow the Arbiter to have a unique action to use unarmed attacks to lower someone WP for interrogation. That has a bit more flavor then shooting walls.
Any other good suggestions we can give for the Arbiters?