It does NOT deal double damage to Undead.
It does heal yourself. (Which is really cool IMO.) That lets you tank really well. Just shoot the enemy in the face to keep healing. (When your at close range.)
It does need a nerf, and I'm sure you will figure out the best way on your own.
It is GREAT for farming money because you get gold for tanking, gold for dealing damage, and gold for healing yourself.
But yeah, only the first one is really a bug.