[Bruno]

It might be worth a perk if they're considered "decoy" hit locations where there are "excess" arms that can be crippled without significantly modifying your effective number of arms.

On the other claw you still loose HP for having them attacked.

On the gripping hand, having more arms (or legs) doesn't make you easier to hit. It might justify buying a higher SM, but that's a separate issue from the arms themselves.