These brushes are meant to be combined with Photoshop's smudge tool on low strength (10-25%). Smudging is the closest equivalent in digital painting to blending and painting traditionally. Smudging rearranges paint and makes it easy to manipulate shades, similar to the power and effect of smudging traditionally. While using the Eyedropper tool in Photoshop is great for blending, using it for all forms of blending and rendering encourages digital dependency in the painting process. The mixer brush is also another dangerous crutch that students develop their skills around. Crutches formed from excessive dependency on Photoshop tools, which can work as cheats limit the efficiency and universality of our skills. Including smudging in your painting process will help maximize your skill efficiency and applicability. 

Get smudging! 

-I