The Magnic cannot compete with a hub dynamo in terms of efficiency, because all it does is to replace the action of friction for a bottle dynamo, with Eddy current action, in transferring the rotation of the wheel to the rotation of the rotor in a dynamo. That transfer, necessarily lossy, is absent in a hub dynamo, since its rotor is rigidly attached to the wheel. The Magnic can have an advantage over a hub dynamo in terms of movability of the dynamo from one bike to another. However, wheels build over a reasonable dynohub can be had for about 60 euro in Germany - I am not sure about the US market. The price and the practical need to keep a dedicated Magnic mount on a bike really tame the incentive to use one. Still, I think it may be fun to employ a new technology just for the sake of it.
This was one of my thoughts, too, earlier in this discussion. But while that loss of energy transfer is a down check to efficiency, it might be compensated by high intensity magnetic fields, lack of mechanical drag, possibly more efficient LEDs and possibly better LED drive strategy (i.e. lower current, more advantageous operating point). I still think it needs a test. I can't do it, however.