I bought black diamond front discs and pads, fitted them myself, bedded in, all seemed fine. After putting a fair few miles on them, I started experiencing juddering at 60-70mph and gradually got worse and worse. I took the zed to Sly at Kaizers, found that the build up of crud on the hub transferred to the disc and put the alignment out. Options were to get disc skimmers out or to replace it all. As I needed the car and couldn't really wait around, Sly cleaned the hubs and fitted new discs and pads, all ok ever since then.
I have black diamond discs and pads on the rear as well, no issues with them.