I've heard a lot of mixed things about these coils from other people that have tried them, but I absolutely loved them. I had one of the first sets in the US and these things were absolute magic both on the track and for daily driving.
They drove way smoother than the Hotchkis lowering springs I had on the car before (smoothness has been the complaint I've heard from people, but they were super smooth for me).
Performance wise these things were top notch. Dialing in these coils with the default spring rates (12kg f / 8kg r) allowed my 255 - 260whp car to sustain tons of grip and easily keep up with the 400whp monsters that I was competing against in the pro am series I drove in. They've got great adjustability, however the only downside is if you want to adjust the damping in the rear without taking the top of the coil off you have to drill a hole in the top of your rear strut brace. Not really an issue, just a pain.