It works, and it looks pretty cool. Panning around the outside of the aircraft, you can see reflections of either the runway surface or the horizon & sky, depending on your angle to the mirror. Especially cool when you look at the inner cowl that is in shadow, because the mirror stays well lit.
However, when you are inside the cockpit and look down at the mirror, what you see reflected in the mirror is the same view you would have of the opposite nacelle from your head position. E.g., if I'm in cockpit and look forward-left-down to view the mirror, what I see in the mirror is the view I would have of the opposite nacelle (just as if I had instead looked forward-right-down).
Unfortunately, it doesn't work to view whether the nose gear is extended, which I understand was the function of those mirrors in real life. Its a small discrepancy, and IIRC has something to do with the cube faces in the 3D representation of the game. I don't know why it doesn't work the way the mirrors work in RL.
I'll post it as a bug.
EDIT: I just remembered - I think it is the same bug as found in the B-17. If you look out the cockpit of a chrome-finished B-17, on the side of the inner cowl you will see a reflection of the interior of the cockpit.
