From The Telegraph:
It produces thrust by using solar power to generate multiple microwaves that move back and forth in an enclosed chamber. This means that until something fails or wears down, theoretically the engine could keep running forever without the need for rocket fuel. (It) defies one of the fundamental concepts of physics – the conservation of momentum –Shawyer invented it over ten years ago but recently NASA said they think it works and a professor at the Dresden University of Technology demonstrated that it produces thrust. Chinese researchers also came up with a working model with net thrust. The picture below (from the Telegraph) belongs in a Jules Verne movie with its coppery plate and myriad bolts.
The concept of a photon rocket has been around for a while, that the emission of photons can generate thrust in space. The thrust generation of the new device has a thousand-fold advantage. Sounds promising. Until the science is known, leave this one in the PENDING file, a game changer if scaled up and understood.