Beware those paint hardeners, they're some vile and nasty stuff that requires the correct respirator to work safely with them.
I know most people like the way paint looks on aluminum boats, but it's a pain to keep looking nice. Always having to put out the dock bumpers and being real careful not to nick or ding the paint, until it happens... the first big ding or gouge, you'll cuss and fuss and may even tinkle your pants a little after you put a nice boogered up spot on all that hard work. The first time I dinged my brand new Tracker, blood squirted out of my eyeballs and fire shot out of my aft end simultaneously! Then that was the end of trying to keep the outside from getting scratched, to heck with it she can wear her battle scars proudly.
A brushed exterior looks good on an aluminum boat and it's an easy application and very easy to keep up.just scrub it in one direction with a scotch-brite pad and she'll look new every time you wash her.