The difference is that the BMW CSL wing blends in with the lines of the car. The one shown looks much more like the old muscle car wings and like the one they make for Porsche 914's.
I will be the first one to admit my error if it looks better once completed. Honestly though, producing an item for a very limited group without any input from that group seems like a faulty business practice to me. Oh well, enough of my .02, good luck to them, I hope I will be proven wrong.
