Never tried "Mirror", watched some tutorials long ago, most of them quite lavish (but more accurate)...
Since i really need a mirror for current project, i decided to give it a try...
Simply put a cam in the center of mirror and played arround with cam-settings (Focal Length + Angle of view)...
Rendered cam and put in Diffuse-Chanel of mirror. Also here played around with settings till it worked (mirror horizontally!).
Quick and dirty,
Animation had NO priority and it took me from 0 (empty project) to 100 (finished result in Hitfilm) ca. 2 hours...
Mirrors are no problem anymore for me, even when the result scientifically is no accurate reflection.
And the effort is really minor (place cam in mirror and render...)
Toystorylab on Vimeo : Crassitudes (my "Alter Ego") on Youtube: