My God I haven't heard or seen one of these since 1988, and it was old back then. Cool stuff. As Bob said, you can't resurface it, and if its used, you'll want to check it very carefully before you use it. Additionally, since it can't be resurfaced, you'll also want to think about how much you plan on using your car.
Keep us posted.
PS My dad had one with a Zoom clutch back in 1968 and loved it. Put his car back together in the early 2000's and looked at a new Zoom clutch - less than impressed.