I used them on my '96 Stumpjumper for years...really liked them too. On the trails I was riding at the time, which were not extremely technical trails, they were great for giving a different hand position (2 actually), but they gave me more leverage when going up really steep hill climbs. I distinctly remember using them to get up this one section of a hill all the time and they helped a lot.

I don't use them anymore on my modern full squish...just seems like the trails are more technical and I am always glued to the grips with a finger on the brake at the ready.