A Hack-a-bit works by pressure on the nose through a leverage. The pressure on the nose and mouth depends on the length of the sides. A hacka-a-bit can be quite sharp because of the leverage and the pressure on the nose and chin. If a curb chain is used, the hack-a-bit is even sharper.
It is very important that the noseband of the hackamore is placed correctly. The hack-a-bit is not suitable for inexperienced riders or horses.