A lip spoiler changes the airflow behind the vehicle by interrupting the smooth flow coming over the top of the car. That interruption reduces lift. The problem with a spoiler, is that they require a specific shape to attain their spoiling effect, dictating styling direction. The C-Class engineers have taken an alternate route to addressing the vortices out back. The taillights act as diffusers, pulling air from underneath the vehicle and venting it out of slits in the lamps. The high pressure air under the car now has somewhere to go, which reduces lift. An elegant alternate solution that achieves the same result as the old spoiler. The air coming out of the taillight lenses also affects airflow along the sides of the car for the better, keeping turbulence behind the new C-Class down. We can't say how close you'll have to ride your bicycle to this thing to get sucked along by the bubble, or how badly it'll mess up your hair when it passes by, what with all that air blowing all over the place, but it sounds like a clever trick.