I have fired buckshot from shotguns at night many, many times at nutria.
It has never limited my night vision or hearing for more than a couple of seconds. The flash is not as bad as it is portrayed on TV or in magazines, as most of it is to the front. If anything, the flash illuminated the target for a quick, successive shot.
Flash from a 20" barrel isn't really noticable except by its illumination of the target. Out of an 18.5" barrel, you see a few sparks, still won't completely ruin your night vision. Any shorter and they aren't much good for anything but entry uses an then your night vision will be ruined by all the other firing (or the lights being on).