I had one of these in my E93 M3....I was also very hesitant to buy one...I thought much like M6Cabrio...after spending nearly 100k and they can't offer it for free? However, I finally found on ebay.co.uk (yes...UK's ebay site had much more for sale, therefore prices were lower). I ended up buying a brand new one from someone who got a free one with their car and didnt want it for $250.
It was the BEST $250 I spent on that car...boy..what a difference it made. When you have a 4-seater convertible, I think its a must to have. You could get on the highway at about 70mph and my girlfriend's hair wouldnt even move a bit. Drop the windscreen and her hair would instantly go flying everywhere. Its actually crazy how good they work. By the way, I was told by a BMW tech that you can actually light a lighter inside the car at hwy speed with the top down no problem....thats impressive!