I purchased this mod: http://www.nextlevelracing.com/stage1.htm Pros:
-Only $50 Shipped
-Very nice guys and easy to work with
-Does make acceleration quicker and could feel the differences Cons:
-Causes car to stall/die at random times
Basically, I thought I'd try this mod. Hell it's only $50. Everything as far as ordering, shipping and installation was easy as could be. I really felt the difference in power especially when shifting gears and in higher rpms (above 3500). I would say everyone should get this for their Bimmer except the fact it causes your car to stall/die at random times. I was on a track making a turn at about 35mph and my car suddenly died. Never happened before chip installation. When I was backing out, my car died a couple of times. Pulling forward slowly, it died. The chip is very unreliable. If this could fix this issue, I would give it a 10/10. Otherwise, don't bother.
One side note, I have been having idling issues with my car which could have contributed to the slow backing out or pulling forward issue. But the turn at 35 mph is unacceptable. Lucky I was quick enough to restart the car and get back in.