fidanza makes one too. It's probably USD.

you can get a stock flywheel down to 2/3 of it's weight safely, and less if you like excitement!

I suppose it's the old saying: speed costs/how fast do you want to go?

you can take weight off other places that the flywheel and have it do the same thing. Lighter crank pulley, use underdrive pulleys on the alternator and water pump.

The idea is to have less rotating mass, some places are cheaper than others to take it out of.