I've used one and they work great. If the water pressure is high enough the legs are no problem. My horse is 17.1 hands tall so it really helps get direct water on his neck and hip without soaking my neighbors, lol
I have one of those and love it. Has a knob to control water pressure and I can imagine it would be good for spooky horses. I've found it really cuts down on wetting/rinsing time. Also, there's less splashing of water, so you get less on your clothes and its nice around the horses face.