I had (and recently sold) an Xtreme light flywheel. It was about 6kgs. Stock is 14kgs if memory serves. I do 90% of my driving in stop/start traffic, the rest is cruisy 80-100kph stuff, and it was a complete pain in the a55hole. Yes, the engine revved through the range quicker, but if ever want to drive the car lazily (ie not slamming it between gears in 1 millisecond), then there were always massive jerks. Makes you feel like you're learning manual all over again..... possibly for months. I couldn't get used to it and went back to stock. I can't express how relieving it is to be able to change gears as fast/slow as I want, based on the conditions at hand, not the car's requirements. Also, on the track (Wakefield) I couldn't change gears smooth enough for my driving instructor, no matter how quickly I shifted the stick and how smoothly/slowly I let out the clutch. I can tell I'll be way smoother when I go back (and smoothness is what you want on circuit). I guess it depends on what you want, and how dedicated you are to it