Pulling on a leverage type bit differentially will act tend to lift the mouthpiece on one side rather then the other as a result of the leverage (just try it), and encourage counterflexion at the poll. The horse may eventually learn to ignore that action, but it's counterproductive and counter-intuitive.
Curbs are not two-handed bits. People use them that way, sure, but people do lots of other odd things too (like ride curb bits on contact). Lots of good horseman talk about how people usually move from one bit to another after they flunk out of one bit, and I've seen it myself plenty of times.
Whatever floats your boat though.