The flaw with Minit Mask was that was generic at best and couldn't be tailored by the color of light like panchromatic film. Another problem was that photochromic glass loses its efficiency over time. But the worst part is that the whole futzing part with the carrier had to be done in darkness, so avoiding dust was pretty difficult. I never invested in it, thank goodness. More sophisticated photochromic masking systems still exist for a limited number of industrial resist applications, but I'd be surprised if they ever catch on in general photography. It's just too easy to do better with pan sheet film, once you get past the more elementary techniques. Of course, many of these options can be used in combination, for those inclined to a challenge.