I am looking for info as to a brand/model of an edger (gas or electric) that
is designed to give a nice, vertical cut along the backside of 45 degree
curbs. There's several that "sort of" work. But, I'm hoping to find one
that is really designed for this application.

I use a powerful electric Craftsman. It works OK. But, only with some
muscle and close attention while edging to keep it going the way it should
be. The muscle goes into keeping the blade pretty much vertical. I'm
actually holding up the outboard side while the inboard wheels and blade run
along the curb edge.