Very nice work for a great concept. It looks like it might look really right heavy, so whatever you are going to put on the left arm, I'd make it look like it has some weight.
How are you going to do hit location. I pressume the right arm will have the hit location of a head, buty will the head too? could the character function if the servitor's head was blown off or will he have two heads. I'd give him lots of armour on the implant head and possibly a force field as the arm location is much more likely to be hit in combat.