Well I'm pretty sure your ski boot goes in them usually you put your front end of the boot into the top piece then push down on your heel to lock into the back piece.
to play devil's advocate... a lot can happen in three months... like the first trimester of school... or an unplanned pregnancy... either way your life is f*cked (see what I did there?) and a lot worse than losing a "U" button.
Dukes should be used for a totally different purpose than these bindings. These are for long hikes and an easy decent. Dukes are for much shorter hikes and shredding gnar. Not to say you couldn't ski some sweet stuff with those bindings, but Dukes can take so much more and are a much more side country binding where these are a long backcountry trip binding