Have driven a few JB clutches. Yeah, no. Not a fan.
My Coppermix twin has done no less than 250 big RPM launches in its life (been in the car for 7 years in total). Pulled it out when I lunched then engine and its going straight back in. No rebuild, no new plates, no nothing. (There is pics of the plates in my build thread)
Feels a tad heavier than standard (esp with the Nismo slave).
There has been many threads about these things. Everyone that owns one won't use anything else. Speaks for itself I think.