OK, so it does not add any horsepower, increase mileage, pile on any downforce, or stands out as a noticeable upgrade. But it is really cool looking. It is the wide angle mirror glass, or "Weitwinkelspiegelglas". Blue tint replacement mirror for the drivers side that the outer quarter of is wide angle so as to reduce the blind spot. Directions indicate that you pop out the old one and pop in the new. Part # 51 16 1 926 845. $36 thru Maximillian. I'll post pics of the install tomorrow.