I have it on my bike and it does make a difference. Especially with bikes with lowered gearing that will benefit a lot from the overrev.
I have mine on a switch, so I can switch between the two at the flick of the switch.
Only two things to note.
1. Stock, or even with full exhaust it does not feel that its making extra power up there. Still very ussable as overrev, lets say to keep a gear between corners, or save a wheelie... With engine mods, I can see huge potential.
2. When activated, it does alter the fuelling throughout the rev range. Even at idle, it is running richer. So really it needs to be set up with a PCiii
on the RR. But I bet this will go unnoticed from most riders. My impression is that the extra fuel, especially down low, makes for a "heavier"/less responsive engine... Now do not take this as a huge problem, as it is not. I strongly believe most people will not even notice.
Also I'm not too sure that it does require extra fuel up there (12-13K). The ECU seems to be doing well on its own. Really it needs to be set up on a RR to make the most of it.