The one huge disadvantage that I don't think anyone has taken into consideration with these is that they're not good for commercial vehicles operating on general public roads as there is no psychological association with some rasping noise that sounds like a dragging brake drum and a vehicle backing up. While a backup beeper may not be directional, it at least carries the association of a vehicle backing up, and makes you alert to your surroundings. I've heard these and my response was to simply stand in place and try to figure out what the hell that annoying sound is, and only realized it was a back-up "beeper" after watching this video. Obviously this completely defeats the purpose of the back-up beeper.