Look in the hub, the end of an A&M crank will be smooth, the end of a Sachs crank will have a small hole in the center...Look at the con rod, a Sachs rod will be copper color, an A&M rod is aluminum or steel color with machining marks on the surface...A&M merely OK, Sachs great..
It will run the same either way, just way longer with the Sachs crank....