> [W]hen main purpose is convenience, if you have to do something inconvenient to use it then you killed the thing altogether.

Funny. Because UV-activated darkening lenses inevitably fail in a half-darkened state, I have a pair of always-dark prescription sunglasses and prescription -er- clearglasses. I can tell you from personal experience that it's inconvenient to carry both and swap between the two as my location and the time of day changes, and yet... somehow there's still a solid market for always-dark prescription eyeglasses.

Weird, innit?