To add to Cactus' comments, the alum slingers are about 700g lighter. So the engine spins up heaps quicker and you get good acceleration gains.
Snitchy posted a video on how to swap it. Good video. Just be careful if you need to use lots of force on the slinger nut. On my 140 I chose to put the engine in 4th, and put a bar thru the rear disc and over the swing arms, then I just torqued the nut loose with a long wrench. Likewise when I put it back on.
Before putting the nut on, I cleaned off the oil, and used a little bit of loctite on the thread.