These are made with "crusher fines." Apparently they are a "waste" product from the rock crushing process.
Crusher fines are of a uniform size (narrow particle size distribution.)
Crusher fines are sharp. They lock together. When ramming these test blocks with the crusher fines you can feel the difference.
Our supplier is looking for a way to get rid of them, and the area soil scientist seems to think they will work just fine. So why not?