You are right about the pitch/cord aerodynamic balance problem. But
such a device would take care of the dynamic balance by far the more
common problem. When you take your prop for balancing to a shop they
only do the dynamic balance. You would have to return the prop to the
manufacturer for pitch/cord problems. But usually pitch/cord problems
are rare - its like having a bent wheel on a car, where most problems
are with dynamic balance.