What I've noticed is that with a bigger motor (say .28 in a truggy), you run the nut closer to flush (earlier engagement)...and if the traction is poor, you can loosen it a little more and make it more driveable.
We ran my friend's truggy where we run the buggies (1.7 mm down from flush) and he was blowing the tires off every corner. It made his motor look very powerful...LOL...but it wasn't so good for his lap times. Loosened it to 1mm and it was all good. I just like how fast it is to adjust.
The biggest thing on the Werks is to scribe the threads on the flywheel nut with an X-Acto knife in 3-4 places and make sure you use Loc-Tite...otherwise, the adjusting nut tends to tighten itself. It was a little maddening at first (happenned three times), but now we have a bunch of them going and they all work great.
They supposedly have a new nut now with an integral o-ring (like a shock collar) and external adjustment slot, but I haven't seen it yet. I'm way happy with it the way it is now.
I've heard good things about the Fiorroni before, I was just wondering how they were adjusted. It sorta looks like my R40 clutch.