Have always used them..
Had em on my zx9r tracky and they saved a lot of damage in a high speed turn 1 acco.. Slid all the way to the wall and only damaged the engine case. Frame, tank and most of the fairings were fine..
I've only "fell down" once on the 10, low speed, and the crash knobs took all the initial impact and protected the tank and frame from damage. It did dig and flip once it hit the grass but it was slow and didn't cause any further damage..
Also helps when it falls over in the garage..
Thats my experience, so read into that what you will..
Others may have different experiences and hate them.. each to there own..
Just don't crash and its not a problem....
Dave
2010 Z1000
ex bikes
05 ZX-10R Race Bike - No.77
95 ZXR750R M Race Bike - No. 75
98 ZX9R Race Bike - No. 000
zx6r, zx7r, GPX750, GPX500, lots of KX's.

I ride way too fast to worry about cholesterol