Sam,
Even though they look somewhat similar, those won't really work as a power hammer. They have a fixed shaft length/stroke. They work only in set circumstances, like punching holes in sheet metal, etc. If you put something thicker or thinner ( like a billet to draw out) it will break the shaft, clutch, or something else. It might work for something like veining sheet metal leaves or similar thin metal work.
If it is at $50, has all of its parts,....and is working,.... I would say get it and find some way to use it. Maybe build a super fancy makers mark stamping press.