I upgraded to the one thats not street legal, so they say, when I installed new cams. It makes a lot of difference because you don't hit the rev limiter of 6000 RPM ( it's now 7000) in 2nd and third gear. I'm not sure you'd see any difference unless you did your cams.
I installed one when I did my 1200 conversion with 10:1 pistons because I needed the 1200 ignition curve. If your bike is stock, I wouldn't bother. As was said above, all it does is raise the rev limit.