A suggestion, based on my experience with the Instax Mini Evo hybrid: Try printing on the monochrome film, then try printing on color film in monochrome, if the printer allows that (I suspect it will, but I don't know). I prefer the look of a monochrome color Instax print over the look of a print on monochrome Instax film. It's a slightly warmer tone, but, more significantly, the "blacks" are deeper and richer, with better mid-tones as well. There will be no difference in permanence, or lack of it, as both are dye-based final images.