Think about it.
Stick anything passive in the airstream and guess what will happen. Fuel injection will compensate for intake air flow changes anyway. Carb system would result in running a little richer perhaps but that sure as hell ain't gonna give you BETTER mileage.
Have yet to see any LEGITIMATE dyno tests. And I doubt I ever will.
With all the misinformation I am surprised there hasn't been some legal action - maybe there has ? For example - Horsepower gains UP TO XXX - that includes ZERO.

If it sounds too good to be true - it probably is.