I think that unless you are trying to do outrageous tork rolls, it's a waste of time. Obviously, you could get some kind of fundamental roll control out of it, [for just flying around] but having that much weight stationed outboard on the wing tips is not a good thing. That's why I thought the best application of this idea would be maybe a small single thruster for improving flat spins and / or for tork rolling a 3D plane.