There is nothing other than a photon engine
Besides, to understand the nature of magnetic field do not exactly requires the special relativity even in the classical time space, they can be explained.
I don't think Einstein was wrong with his formula, but he certainly altered the explaination so that some misunderstanding followed up.
The most probably reason for a misleading understanding might be not to let the general people to understand the nature of physics.
However I think the EM drive is therotically impossible. A photon engine is more reliable than this one.