I'm not sure how Sachs performs for Bimmers, but on a VW Golf I had, I thought I'd save money and buy a Sachs, and it was crap. It lasted 2 years and 75 000 km, then I put an OEM from VW and it went the rest of the life of the car which was another 220 000 km when I sold it and as far as I know the next owner used it until he parted the car out 3 years later!!!! Just my two cents, you might save a little at first but it's going to cost you more in the long run.
BMW 325I E30 Chumpcar Race Car
BMW 540iT M-Sport (New Family Hauler)
BMW 135i Msport Daily/track toy