Do yourself a favour and forget about the BMW branded ones. Some people say they prefer the styling as the bars don't hang over like the Thule ones but for the extra premium it's not worth IHMO. I personally prefer the hangover as it better for loading and increased space for roofbox + bike racks etc etc.
See my previous posting with Thule aerobars which I carried over from the E91.
http://www.f30post.com/forums/showthread.php?t=781735