 In the daylight, it works like an ordinary mirror, but at nighttime it works like a strobe.  In city driving each time you pass a lit sign it decides whether to darken or stay in daytime mode.  There's a lag time in its transformation, resulting in blinding light reflecting in your eyes when you pass a sign, followed by the mirror darkening, then going back to daytime mode just in time for the next lit sign, thus blinding you again.  On the highway, when a car is directly behind you the mirror stays in the nighttime mode, when that car changes lanes the mirror switches to daytime mode and you're blinded by the next car until it gets close enough to activate the nighttime mode.