My friend uses them on his R32 GTR. They seem to be pretty good and he tracks them relentlessly as well. I don't like the fact that with most aftermarket caliper companies, you have to use their proprietary brake pads, due to their caliper shapes.
This limits you to brake pad companies/compounds which is why I like using Spoon/NSX calipers. You literally have an infinite amount of choices as the pad shape is OEM.