I have KW V2 on my E60 that I bought bout 1.5 years ago and as of today, it leaked twice. Yes twice, first was due to high impact (damn potholes) and second was just leaking. I have put bout 80k KM on it so far.
Performance wise, they're great coilovers but given an option I think I would look for another option (Bilstein).
Reliability wise, they are not the best (KW) and they can't really withstand impact such as potholes that caught you off guard.
But then again, this could just be issues that I had with the particular product. Other than that, I love the ride, drives like it's on rails and it gives so much feedback to the steering wheel.