I think that means that if a horse tends to be high headed, it will bring his head down (youıd bring your head down too with that kind of hardware in your mouth) -- and once his head is down, you have a better chance of his moving in a proper frame. Thatıs exactly what happened with my first horse, which is why it worked so well with him. But Zara did everything in his power to get over the bit to get away from it. And trotting down the trail with your horseıs head tucked into his chest is only marginally better than going down the trail with your horse looking you in the eye!
The bit will certainly stop a runaway.
Hope this helps.
Nancy and Zara from Maryland