"He says that the thrust drops off rapidly once the generator starts moving along the line of thrust"
So, he claims that he has falsified Newtownian physics and relativistic physics.
Of couse, you can always get off the planet real fast by stopping. Just make sure you know what direction the planet is headed first.
Note that there ARE propulsion systems that don't have reaction mass in the conventional sense. The closest one would use magnetic effects to push against the Earth's magnetic field.