Not all brake rotors are created equal. These rotors are cast to very high material specification and tight tolerances. The slots extend brake pad life by "wiping" the white-hot boundary layer from the disc and pad, increasing braking efficiency and extending pad life, and they have ramped edges to cut down on noise.
The rotors have a zinc plating to keep the rotors from rusting outside of the pad contact area. This is friendlier for pads than cadmium. Factory size, these are a direct replacement for stock parts. Sold in pairs.