Slightly costlier ( $35 vs $54 in a popular chain for 2005 Camry front) rotors do not rust. But does it come at a cost of performance? The surface might be more smooth and hence have less friction during braking.
I had to search the internet on this question; It appears to be a gimmick. that is no substantial change from standard rotors. I found two different techniques : One , coat or paint the rotor , this protects the non-wear surfaces from rust . However , about the only rotor surfaces that can be seen are the wear surfaces ( with the wheels on). It would be much more noticeable to paint the calipers. The second type was to carbo -nitride the standard rotors. This is a surface treatment that puts a very thin , very hard layer on the iron. This hard layer might give better wear resistance but the mileage they claim is what I am presently getting with standard rotors. They also claim some corrosion protection but as a professional corrosion engineer I have never heard of a carbo-nitride layer being used for corrosion protection and would expect only a minor affect , if any. Carbo-nitride is traditionally used on items like drill bits. There were various vague claims of "alloy" and chrome but nothing specific so apparently they were talking about the traces of Cr, Mo, and Ni that are in all modern steels and irons because of recycled scrape.