It does work, with a little elbow grease on really stained aluminum
I recently purchased a 1993 18 foot Lund that had been sitting on a lift or tied to a dock for its entire life.  Of course that meant the bottom of the boat was stained.  My hope was a spray and a rinse, but nothing is ever that easy.  On the very soiled sections of the hull the product did help, but only with a green 3M pad.  The cleaner part of the hull also needed some assistance with the pad method, but a lot of the gunk did come off.  I would say the product helped clear up 60-70% of the hull, making the boat look much better.  In my opinion the product did what I needed it to do, but it did not make the boat look like brand new.  I am not disappointed in anyway.  I would purchase it again.  I did apply three times in hopes it would work out a bit more, but sometimes stained is just stained.
Rating: 4 stars