I teach a modern physics class to high school students, which includes a unit on special relativity. I gave them this as a bonus exam problem, and I’m pleased to say they all got it right. It’s not hard to prove that, whether the proposed virtual particle radiation is massless or massive, it is not feasible. For massless particles (photons), the drive would have to use 600 times more power than is reported. For massive particles, (like electrons and positrons), the particles would have to be moving at 600 times the speed of light to produce the reported force at the reported power.
See this PDF for the proof.