Race rails are good, and the no-cut sliders are too.
The no-cut sliders are on a solid bar that goes through/under the frame.
Even if a slider breaks off(which alot do), it has usually already taken the brunt of the impact.
Rarely do they save your plastic, but can help prevent other minor damage.
Sliders that have to have holes cut aren't the best way, because you don't know if the guy you eventually sell
the bike to wants them...or the holes in the fairings.
Personally, I hate sliders, they remind me of training wheels.
I've also seen a bike with them slide down the road, and have minor damage...until the slider bit the road good, flipped the bike, and tore it all to pieces. Enough cosmetic damage ends up totalling a bike most of the time anyway, just from excessive cost.
Sometimes that's a good thing too.
Pros and cons to everything.