ok. I have confirmed with GraniteStone that a mitred edge runs the entire length of the edge where the downturn meets the benchtop, not the corners.
So, I have been quoted for 3 joins on the corners like this:
And it should only be 2 on the edges where the top joins to the 2 sides, like this:
Im glad I looked into it further as I just saved $230 bucks. :)