Top feed air filter good/bad

I have yet to read anything about them, but had planned to use one. I planned to build an air-box because my hood scoop is functional. I am guessing if there is a turbulence issue, then maybe one of those crazy "gas mileage" "turbine" things, (diffuser) that redirect air flow, may not be a terrible addition? I never bought the gas mileage increase aspect, but I can see how it may redirect flow into a better more organized pattern.

My next question would be have there been legitimate tests to prove that there is actually turbulence? That's a damn hard conclusion to come to by just looking or "feeling" the difference in the performance.