I don't have experience with this part, but from the part's description, it's claiming to "swirl" the air and make more power this way. Unique grammar aside, I will say that, in general, if you're looking to maximize airflow, you do not want airflow to become turbulent. You want it to be laminar, so that the flow is smooth. Swirling the air will make it turbulent, and you don't want that.

And I don't know why it would be illegal, either. Feel free to try it out.