I wish that rear spoiler was maybe half the height, more than stock but not this high. IMO it's too tall. I don't care what BMW says about the aerodynamics as the stick Gurney flap already has a proven benefit. If I wanted a poke in my eye and the downforce to go with it then I'd get a wing.
What about a rear diffuser? That would clean up the rear very nicely. I like the new IND/Challenge diffuser.
Just my opinion.
2015 BMW M5 Sedan M-DCT w/Competition Pkg and Carbon Ceramic Brakes, Driver's Assistance, and Executive Pkgs, B&O, Alpine White / Sakhir Orange and Black Full Leather, lots of carbon fiber, and a Trunk Monkey call "Der Stig".