I bought this for track days. It is comes with a NA Miata rear-view mirror that it's clamped to, but you can attach it (temporarily) to your own car's rear view mirror instead. The ball and socket joint on the mirror needs some more friction, as it tended to flip down on its own due to the weight of the mirror under hard braking. You could probably fix that by pouring some sand in the joint, or clamp it to your own mirror that has a stiffer joint.
$10 + shipping from FL.