The tornado thing is junk. In a modern fuel-injected car, the swirling effect would have to be sustained through the throttle body, into the intake manifold, then split up into a mini-tornado for each runner (cars have 1 and sometimes 2 runners per cylinder), then keep spinning as it passed through the fuel injector spray, through the intake valve, and into the cylinder. Yeah, right. I guess it's possible that it could help on an old car with a carb or throttle-body injection since it would be placed close to where the fuel/air mixture takes place, but I doubt it. Like someone else already said, if mileage could be increased with a 50-cent piece of metal, every car in existance would have it from the factory.
When all the gas stations in Florida kept shutting down because of the hurricanes, I decided to try doing the speed limit and accelerating as slowly as I could possibly stand (like a normal person, and with upshifts at 1800 rpm or so rather than 4000+). Gas mileage went from 16 to 20. I was impressed, but quickly lost patience.
Changing your driving style makes a pretty major difference. I suspect that anyone who thinks they've seen gains from the tornado gimmick are actually doing so because they drive more conservatively to "maximize" their mileage gains.