This is a pic of the one I have. It shows the extent of the view behind. Taken this afternoon but stupidly, I didn't measure the width of the mirror. I would guess at 10"" and yes it does does stop the visors going full forward but I can live with that. If you know you're going to drive into the sun for many miles you can just flip them forward and readjust the mirror.
One out on the road with cars etc would be better!