APS brake discs are state-of-the-art CNC machined from a one-piece forging.
When the metal is forged it creates a directional grain flow that follows the contour of the disc. This allows for a much stronger disc that has a reduced risk of the cracking and catastrophic failures associated with the inferior welded design.
The APS "Black Steel" advantage is a proprietary heat treatment with a two-fold purpose. The heat treatment strengthens the steel by bonding the carbon, oxygen and nitrogen in the top layer of the metal. This is not a coating that can wear off. The steel itself is transformed. The heat treatment gives the steel its aesthetically pleasing black appearance and provides a surface with a high resistance to the corrosion and oxidation associated with the extreme thermal cycling experienced in aircraft braking systems. This makes it an excellent choice for agricultural aircraft that work in a harsh, chemical environment, as well as anyone who leaves their plane outside for most of its life.
I actually ordered wrong disc for my C172 and had to return them. Spruce was accommodating and return was easy and correct disc were sent out quickly.