Looks like a great plan. I posted some suggestions for HSTs awhile back. I struggle with them and don't like to take the time to draw that line either.
So, I bought the triangle for making HSTs and have been using the past couple of weeks. I love it. No more hoping to get the line right on the corners. No more cutting the 1/4" off when sewn. I do trim to make them perfect but I don't even have to oversize them.