They fit in here to give a total out of combat move bump as well as an in combat move bump. Sale with zeal, although that is there for the extra crit chance, which can be upgraded to a phantom dancer.

As far as that goes on this build, you can change it out for a black cleaver. Nothing wrong with that. What you want to make sure that the attack speed is high, snf you are using their life total against them with each hit.