Just did the Dinan springs installed by local BMW dealer, I was deciding between ACS & Dinan. Prefer the ACS drop which I think it's about one inch all around for RWD 550i, but since the local BMW dealer gave me a great deal on Dinan parts and labor I decided to go with Dinan and have a peace of mind that the install is done by BMW dealer.
My initial feel is that the Dinan springs drop was too minimal (only around 1/2 inch) and in the Comfort & Sport mode I cannot really tell much of difference vs. the stock, i.e. still very comfortable ride with some body roll on corner. I have not tried in Sport+ mode and driven the car too aggressively yet.
Anyone else out there with Dinan and can share their thoughts, thanks.