Square keeper does look ugly to me.
I don't disagree about it being tried and true, most army stuff is i know, but in my experience in the infantry all the army provides is not generally good quality or expensive.
I suspect they went with the material keeper for cost and function, no shine and no clanging of metal keepers.
I quite like the idea of this one, though in a single piece design. The one you show really is too utilitarian for my taste.