Is true that the energy put into the system (in the form of the dynamic mirror) must be the same or greater than the energy of the photons taken out? I don't think this is the "zero-point energy" or "reactionless engine" breakthrough that people on that page are hoping it is.
Yes. Bear in mind that each individual photons carries very little energy - the energy required to generate the described 'mirror' is enormous by comparison.
The main value of this is further experimental verification of certain aspects of quantum physics, as mentioned at the bottom of the article.
