Sorry for this late post but I think the OP was just recently re-published by Jon and it's the first time i have seen this.

1. The roller end of this clamp can have a "V" cut in it greatly facilitating holding round stock.
2. Softer roller material can be substituted for compatibility with softer alloys. Same as putting a piece of copper/brass under a step clamp but less hassle.
3. Various shapes (octagon, square, etc.) could be substituted to fit part features more securly.
4. Dowel (or roll) pin thru the "roller" to fit into a feature-hole to locate part x,y origin repeatedly.