personally i would not get O'Brian to do it... try and get the OEM ones from BMW and have them to fit it..I can assure it wont feel the same if you get it from O'Brian..
I had a Lexus IS200 which got a OEM windscreen, replace by O'Brian with there glass and the first week, i had little stone chips and window seals were all lumpy and wavy!
now Im rolling in a 135i