I had one installed by a shop here and when they put it on, just like the instructions say, it might require heating by a torch for the holes to line up, and it did, thats why I recommend anyone to have a shop do it if they don't have air tools and a torch.
As far as performance increase, it does rev faster and my idle up seems better when I use the A/C.
As far as power to the rear wheels, theoretically less rotating mass = more power to the rear which happens when you lighten up the driveline etc.
The horsepower from the engine will not change as the HP is measured at the crank and the flywheel is after that.
You will have a slight HP increase at the rear wheels by lopping off around 10 pounds of rotating mass but with out a Dyno to test my car on I can't really say how much.
I have noticed that when I put the flywheel on with a new stock clutch there is more chatter when starting, so I would recommend also to upgrade the clutch but don't know which one to pick.