I have always used those sharpeners that you drag through the little slot. I always felt like I wasn't getting great results - maybe from how I was holding the knife.

This eliminates that and just couldn't be simpler. You could sharpen your knives with one hand while doing something else with the other. Just insert the knife, pump the slide a few times and you're good. 

I haven't tried it with my other brands of knives. I hope it won't damage them. If it does, then this sharpener would really only be useful if you want/have all your knives in the Ninja ecosystem.