A mass solution, once put into a transfer orbit, requires no further energy input and can be used again and again.

In fact, a large, heavy one can be created or moved into such an orbit, then Mars/Earth journeys only need small, light ships to dock with it at each end.

Except that magnets don't deflect neutrons or gamma rays. Seems like you would need some amount of mass shielding in any case.

Hmm. How hard is it to get superconduction in space? Its not like it has to be room temperature.