The claims they say are a .33 second increase in the 0 to 60 time of a car with the stock ignition system. In other words, the test car might have had a bad coil, might have had a bad wire, could have had high miles and the coil and wires needed to be replaced anyway.
As far as gas mileage, they never make a concrete claim, they simply say it will make your gas mileage better. I can sell and install for you the most effective tool ever to improve gas mileage, I'll bolt a block of wood under the gas pedal.
Point being, don't believe everything someone claims on a website about a product.