Most blending brushes are narrower and elongated, making them more directional than Paula Dorf's Blender Brush. This Paula Dorf tool is fairly large- you can see that it's even wider than Bobbi Brown's Eye Sweep that was designed to apply base color all over the lid and crease. As a result, unlike many blending brushes, this one will definitely not fit in the crease and is probably not suited for those with limited lid space.
However, if you're looking for a brush that can diffuse color in one stroke, not push color around and will not mess whatever you did prior to blending, the Paula Dorf Blender is an excellent option. I also use it to add a light color all over and sheer out my application if I think I overdid it. The brush's size and fluffiness also allows for cleanup under the eye and highlighting (though I admit I haven't been using it for this purpose since Hakuhodo brush appeared in my life).
Paula Dorf Blender brush is made of natural hair (I'd guess goat), it's soft and just dense enough to hold its shape and perform relentlessly.
Bottom Line: An old reliable.
Paula Dorf Blender Brush ($30) is available at Henri Bendel in NYC and dermstore.com.