I know what it is meant by inertia. However, it doesn't mean
that it is any more efficient. This is because the magnetic force
can work both ways; it can assist in moving, and it also can stop
you from moving. In that sense, it is still rather inefficient. The
main novelty I can see from this device is not in generating energy
off hand, but rather, harvesting "wasted" energy from things
already moving, ie energy scavenging.
Gravity will come into play in both hand dynamo and your device.
However, remember that gravity field works both ways too; it pulls
both sides down, and thus it will not play a part at all here in
generating energy. Totally none.
With regards to magnetic force, refer to above 
Ok, I have to say that your concept is totally wrong, net gain
in energy can never ever be more than energy input. However, I
guess that it is your phrasing that has the problem
The main way to be more efficient now is to have a larger torque
and a lighter wheel weight, both of which can be potentially
achieved by your device. And yup, the main thing is scaled up...
Your device should not be as big as a commercial windmill; an
extreme amount of magnetic torque is required. In addition, being
smaller means being able to fit into more places, which might
actually be more efficient.
