The only thing I've heard is the Magnesium wrench is softer material and no supposed to wear-down or leave scratch marks on the roller nuts. Also using the "big" Magnesium wrench does provide a bit more "cheater" leverage as that sucker is looooonnngggg.
Having said that, I've recently made a DIY stretching table, along the lines of Northland's, and use 3 crescent wrenches.