Power = thrust times velocity. If this has constant thrust at constant power no matter what the speed and doesn't require propellant, then at the speed of powe

Power = thrust times velocity. If this has constant thrust at constant power no matter what the speed and doesn't require propellant, then at the speed of power / thrust it's working at unity and over that speed it actually generates positive energy. There is already a reaction less drive, photons. The unity speed turns out to be the speed of light. It is also very impractical as thuster since it requires so much power per unit of thrust.