I USED to use them on my 990 R, however after a nasty high-speed offroad fall I found on a big enough impact the rear mount can pop off the frame, and ends up dug into the rear cylinder block. I had the SW-Motech ones with the cross-brace. When this happened the cross-brace also dug a nice gouge into the oil tank.
They add tons of weight, ugly, and most importantly - these bikes crash WELL out of the box. Most people use them as a reflect and protective action. I've crashed with and without them, and had less risk of serious damage when they were on. My crashes without them - the bike slides better, is lighter, and those plastic lower guards on the 990 work really really well.
For road only use, maybe they are fine. And I know they are good for "car-park tumbles" - low speed crashes. But IMHO for really gnarly falls, they suck.