I had the FX350 with lightened steel flywheel for about six months until the boss (wife) couldn't take it anymore and I had to go back to stock.
My impressions: Clutch take up is a bit abrupt but ok once you get used to it. If you live in a metropolitan area with heavy traffic, you'll be better off with one that uses the stock flywheel. On the performance side, it took everything I dished out. Countless LC starts plus FFS and never a slip. The engagement when power shifting is positive. You can feel it put down the power faster.
Car at the time had GTX2867r putting out 400whp. Both passenger and driver side JBR 70a duro engine mounts plus a MFactory helical LSD. Tires: Michelin PSS 245/40-18