Well,Shawyer's drive would appear to defy Conservation of Momentum. That would require extraordinary evidence to accept. Wikipaedia tells us:
"According to Costella, the angles of the force vectors are calculated incorrectly. You can use high school physics to find the correct angles and reach the conclusion that momentum is conserved and the drive can't work as postulated. He says that the rest of of the paper has theory that is correct, but which doesn't demonstrate anything about how the drive works."
"Shawyer has since published an updated theory paper (version 9.4) where the diagram criticized by Costella is simply omitted. Yet it should be noted in this debate that Shawyer does not compute theoretical thrusts subtracting vectors off a diagram, but uses thrust equations whose derivation is done from Cullen's work involving wavelengths, frequencies, group velocities, Q factors, relativistic law of addition of velocities, and so on. As a consequence, a valid refutation of Shawyer's theory would show where the maths are wrong."
"Dr. Costella avoided providing a scientific analysis of the equations and basically answered on his blog that he didn't have time to find a possible mathematical flaw in the papers and suggested a simple graduate student should do it, ignoring the fact the papers were already published in three scientific journals, i.e. after validation from referees.
As Dr. Costella implied, Shawyer may have incorrectly identified the forces on the sides of the waveguide. If an error is present, it is most likely that the thrust is eliminated and the drive then cannot accelerate. Following this hypothesis, the Chinese team would have done the same basic error, and their positive experimental results correlated with their theoretical predictions would be another coincidence."
Hmmm. I would like to know why Costella, who is apparently am authority in this specific area, has not debunked Shawyer's calculations if as he says a graduate student could do it. I would also like to know how this drive could be expected to work if it's design is based on a flawed model, which Shawyer appears to accept as such since he has removed the offending diagrams from his paper.
I'm not going to get too exited until those points are resolved.