Just to add a comment that I received in correspondence with a 10 victory ace who flew P-51As, Spits, P-47s and P-51Bs - he said rear view mirrors were virtually worthless in real life combat. Others have also said that if you actually saw something in them it was too late already.
Another free sim does a half-way job of modeling rear view mirrors by displaying a sky-like image, that displays movement, but that is not the actual view aft. So it gives the illusion of being a functional mirror, but you can actually see nothing real behind you, lol.