They do work.
I have the Shogun frame sliders, and have dropped by bike twice (both times at a standstill). One drop was in a gravelly alleyway, and the other in a parking lot. If I hadn't had sliders installed, I would have at the very least scratched up my fairings and turn signal trying to lift the bike back up. After both of these drops, all I have to show for it is a tiny gouge on the bar end slider, some scratching on the main slider, and the tinest (1cm long but very thin) scratch on the tail fairing.