Michelle Obama’s Harmony Ring

As far as I know you can’t use hard cheese in it. I was wondering what the blades are made from because that is important too for holding up and not rusting. I did not find on their listing what the blades are made from. I own the kitchenaid attachment for my mixer and it is made of steel, it works very good BUT this one looks a little more convenient. Hard cheese is usually done in a blender type thing such as Vitamix etc. Hope this helps