Pushes selected guide hairs toward a perpendicular orientation to the surface. The bias for this tool is closer to the root of the hair than to the endpoint."
Sounds like the effect when using the surface attract tool set from -1 to 0?
It´s similar, but not equal. The atract tool moves a lot the endpoint of the curve, the 'Puff roots' tools would act like a gradient, affecting more the base vertices and less the tip vertices. I guess that the atract tool is more like a kind of reset tool.
The problem is that when brushing the curve we tend to flat it over the scalp.
You also could provide the option to retain or not retain the curves lenght in the puff roots tool.
Finally I want to report that under Windows7 64 bits the slider of Style>Comb Brush Settings>Fallof is not responsible, we need to set the value manually editing the field.
The figure that is attached will illustrate better my request :
Click thumbnail to see full-size image