probably most anything you saw on a street car is a gimmick, is why
Ferrari's street car diffusers are one of the only ones that actually work. Here's a 430's, it looks steep here but i think that's just the end of it plus a weird angle of the photo, i've seen it in real life and the beginning is quite shallow and gradually becomes steeper. the whole piece is maybe 2 feet long:
here is a real, 100% working racing diffuser. Note the angle. This is more like what kind of angle actually works.
