I have never heard of such thing. Energy is produced inside the engine which causes the compression to move the flying disc. Not in the tailpipe as he claims, even if his thing burns the unburn fuel in the tailpipe, it will throw away that extra energy. This guy wants to give you 4-month trial, not even for a second will I try it.
Some people believe they can increase the mileage through a magnet, that's another phony theory. You can tell from the uneducated sellers.