The success of this device depends one enourmous assumption - Air / Fuel mixture in your engine is not sufficient AND this results in less than optimal power. I know a fair bit about physics, and let me assure you, in modern engines (produced after about 1920), this is simply not true.
A couple things he should add to his FAQ page:
Q: Will this work with my diesel engine?
A: No, it doesn't work on any engine, and certainly could not on a diesel as the fuel is added directly to the comubstion chamber. Creating a vortex in the air intake system would have no effect on a diesel engine.
Q: How does the vortex remain in effect as the air passes through the complex shapes and curves of a modern carburator?
A: It does not. This device will increase your performance in the same way a large "Powered By..." sticker does.
Q: How does the vortex improve air fuel mixture when the throttal bodies and fuel injector nozels of modern fuel injected engines have already been designed to provide optimal fuel / air mixture?
A: It does not. And even if it did improve air fuel mixture, the increase in power and fuel effeciency would be imperceptible. In fact, the random turbulance that results from the air being sucked into a combustion chamber and compressed by the rising piston, then on the following stroke ignited, is such that almost no "pre-mixing" is necessary.
Q: If this thing does not work, how do you stay in business?
A: I rely on bad science and ignorance to trick people into thinking my device works. Also, by preying on the poor boy racer who can't afford real performance enhancing products.
Q: The device looks so simple, why do you charge so much for it?
A: Although my device costs only $2.38 to manufacture, I have found that products priced between $50 and $100(K&N, et. al.) are perceived as legitimate, yet still sell in high volume.