I have had the HKS exhaust for some time now. I don't have the blued tips. At first the sound did not "match" what I expected. After several hundred miles it really came into its own. Cold starts do have that "evinrude" tone, when heard from outside the car. After it warms up it is very mellow. No drone or extra vibrations from inside the cabin. Sad it's been so cold and wet lately. I enjoy the windows down by 1/2 listening to the mechanical symphony. Alignment has remained spot on. All joints have remained tight. Mine has the HKS logo cut into the rear brace. The finish has remained perfect. The stock package is good. Its one piece design was impressive. Comparing the stock unit to the HKS, with its mandrel non crimped bends, it has to allow some extra flow. I find the upgrade just another way to personalize my car.
07 335i coupe, manual w/ SSK, clutch delay delete, Procede, K&N drop-in, CPE downpipes w/ high-temp coating, HKS exhaust, BSH-OCC, ETS-IC, CPE charge pipe, Tial BOV, M3 suspension upgrade, rear lower X-brace, Hankook rubber, LED interior lights, LED license plate lights, Royal Purple since break-in.