It doesn't. See Carnot. The greater the temp differential, the higher the thermal efficiency.
Unless "efficiency" is relative to the best theoretical efficiency under a given temperature differential. Even then, it's easier to get high efficiency with high temperature.
This technology is sold as low emissions.
This isn't disruptive technology on the prime mover side. Maybe some on the power generating side, with the linear magnet the voltage woul dhave the same periodic regularity inherent to rotating machinery.
This new technology would need to demonstrate increased efficiency over existing thermal generation units. Until then, I will wait for data supporting such.