I've got the same clutch as John^^^ did a heap of launches at a cone racing day without a prob but toward the end of the last cruise I did a huge launch crossing Tonkin on Welshpool Rd, slipped & stank like a pig but was fine 5 min later when I had a run with a Lotus & has been perfectly drivable since, don't know if the slip was caused by 280Ks of hammering or the 6000 launch but for the price they seem pretty good value.
As for the clutch judder, on a previous car I had I got very bad judder soon after an engine re build with a new clutch, turned out the rear seal was leaking oil onto the clutch plate somehow & was the cause of the prob, dunno if this can happen on a Subi tho.