I was in the rack marina business for 15 yrs and the "aluminum brightners" and mag wheel cleaners will do a great job on the aluminum,but,they are a weak acid and as such will go after the zinc plateing on all the nuts,bolts,washers that they come in contact with.I used it for years on my snowmobile suspensions and tunnels too,and after 3 applications enough of the zinc plateing was gone that the rivets and fasteners started to rust. I eneded up replaceing everything I could with stainless,but that ended up being worse because they would leave a black stain on the aluminum that I couldnt get off. On the pontoons at the marina we didnt worry about the fasteners rusting because after 4-5 yrs on lake erie the whole boat was pretty much junk anyway.
Another thing is that the acids will go after any painted or powdercoated parts on the motor and leave them either streaked or semi- gloss,and eventually chalkey. It would turn the decals on the pontoons white after a couple years.We did use the Zep product too.