I have the UUC Stage 2 Lightweight Flywheel w/ OE M5 clutch and pressure plate. I love it. The car is much livelier with the setup - revs quicker, more positive feel from the clutch pedal.
You get a small increase in clutch pedal stiffness, and an increase in clutch friction and holding power. The setup left me with better driveability. It is easier to modulate. The increased holding power lets you get on the gas quicker and have the clutch grab and take it, instead of slipping so much before grabbing. The car should have come this way from the factory.
I like the solid flywheel (as opposed to OE dual-mass). The upgrade removed the driveline shudder I used to get from the worn flywheel dual-mass spring mechanism. The sprung-hub clutch also does what they say - eliminates gear rattle. I got no noticeable increase in gear rattle after the upgrade. My exhaust is without muffler and one resonator, so perhaps it drowns out any additional noise. But really no difference. I run the thicker Redline MTL.
Overall, an excellent kit and very worth it.