I can't see much use for this thing for anything other than a mentally disturbed individual who has barricaded himself. Flash Bangs work because they overwhelm multiple senses of the human nervous system, not just the eyes. The tremendous noise, flash and particularly the pressure wave of the NFDD can be effective, but even that is not a sure thing. I have never seen or heard of a suspect being released and charges dropped because of police use of NFDD.
I can see its uses for training, not for real world application though. Our training and safety policy precludes a lot of stuff being used on roleplayers, combined with things like iTESS (enhanced MILES) or Sims I can see it having a place. In prisons where the dolphin huggers would be all over you for using some things on prisoners then it might be a good tool.