Photoshop Dual Brush

I was intrigued by the Photoshop dual brushes, but I was unable to find too much information about them.

I notice they combine two simple brushes through the use of a blend mode.

I can combine two brushes through a blend mode myself directly in Photoshop without using dual brushes if I want some kind of static new brush footprint. What I want to see is a brush behavior that is unique to dual brushes, and that cannot be duplicated through the use of a specially prepared combination brush sample.

The hard mix blend mode has a threshold behavior. It forces grays to either black or white. I wanted to see if I could use the hard mix blend mode and a Photoshop dual brush to create a brush that has mode bristles when I apply more pressure.

Not darker bristles. Not a bigger bristle footprint. More bristles in contact with the canvas.