Not sure if it's news, but the Drop in K&N filters are rolling... Same as Dinan but black instead of blue rubber and red instead of blue element.

I just bought one direct from K&N since nobody in Phoenix besides BMW have any filters of any kind for the 07+ z4...(and they want 28 bucks)

But hey stock filters are only 14 bucks from realOEM and the K&N probably isn't much of an advantage for N/A Si... removing the carbon second filter only gets you 1-2