What are the "pros" and "cons" of using a hackamore?

A hackamore is like a halter in that it puts more direct pressure on the horse’s face (nose, side of the face, or chin) and creates a direct response. For example, when you pull straight back, the pressure is on the nose, and the horse should step back away from it. Pulling on one rein to the side creates pressures on the side of the face that the horse can move away from. So the pressure of a hackamore is a natural pressure that horses learn rapidly. A bit creates pressure in the mouth regardless of how you pull it, and the horse has to learn the more subtle signals of a bit. On the negative side, if constant pressure is maintained with a hackamore, horses tend to start ignoring that pressure more quickly than bit pressure. Therefore, constant pressure should never be maintained with a hackamore. Pull-and-release methods of training are essential when using a hackamore. Since the mouth is more sensitive than the nose, constant pressure for head setting and collection are more acceptable with a bit.