Both the aluminum, and the stainless, have there individual advantages. The purist will favor the aluminum for its original appearance, both the aluminum, and stainless, are polished, but make no mistake, the color of the luster is quite noticeable to the trained eye. The fenders are of the C shape, and all are after market now days, the NOS are gone. The after market fender has to be fitted , not a easy task to get it right, any one who has under gone the drill will agree. The rear after market fender is a battle to get right ,the radius needs to be greater, I have over the years, fitted some 40 fronts and rears, so I speak from experience. If you go to the Vincent web sight , I wrote an article on the step by step procedures that I use for installation. If you choose the aluminum fender , make sure you seal the reinforcing straps, it is also a good idea to paint the straps. The reason is to prevent the two unlike metals to form electrolysis points, which cause the aluminum to corrode . Road salts between the straps and the aluminum cause rapid corrosion, seal with 3M upholstery / welting glue. The main plus in selecting stainless over aluminum is, durability and its resistance to cracking, and ease of maintenance.