I saw one of these recently in a Man At Arms video I believe. They were making Link's shield and they used this to build the curvature of it. Very impressive to watch the craftsmanship that went into it just working that relatively small piece.
Is there a variation of this rolling hammer that is a drop style hammer? I seem to recall seeing them use that on Orange County Choppers to shape curved pieces. It was basically a rounded mandrel with a motorized hammer going up and down over the mandrel and the guy worked the material in the same basic manner as they did on the rolling hammer.