Rollers are round, Sliders are not.
I don't know really, I think that since sliders are already not round they work longer, since rollers get flat spots and stop rolling at some point. I'm switching to sliders. My scooter has over 6000 miles on it and I think the rollers have developed flat spots. Sometimes it will delay up shifting and sometimes gets stuck in "high gear" if you will from a stop.