I have got the request for explaining and comparing bitless bridles. It may surprise you to know what I do not endorse all bitless bridles as a "good" alternative to a bit. Some can be worse than a very severe bit.
When I look at a bitless bridle I see it as a way to train and enjoy your horse without intentionally (pulling back on the reins with a bit in the horses mouth to stop him) or unintentionally (the horse getting loose and stepping on a rein, causing pain from the bit without the rider in the picture at all) causing pain to the mouth, which is the most sensitive part of his body. I know the horse is responding to my commands, not the pain the bit can create when I am bitless. So basically when I look at bitless I am looking for a bridle without a bit that creates communication and understanding; not pain.
However not all bitless bridles are equal, better than a bit or kinder than a bit.
Today we talk about mechanical hackamores. They are one of the most common types of bitless bridles. Hackamores consist of a usually rigid or textured noseband, shanks of some sort that the reins attach to lower than the noseband and a curb chain or strap.
To clarify: A bitless that does not have shanks or a curb chain that tightens on the mandible (lower jaw) when the rider tightens the reins IS NOT a hackamore. This is a side-pull or bosal. You often have "english" hackamores but really they are just a nose band with rings on the caveson. They act on direct pressure on the nose and face, therefore they are a sidepull. A bosal is a rawhide, leather or metal teardrop shaped noseband that works off pressure of the nose in a similar way as a sidepull but the reins are placed on a knot at the bottom of the teardrop. A bosal also works on poll pressure along with nose. Rope halters and nosebands made of rope are not hackamores. They either attach the reins with rings at the noseband and are sidepulls or attach the reins on the lead loop and have the same stopping action as a sidepull but the steering of a bosal. See the difference between these commonly mislabeled bridles?
Back to hackamores.
There are two reasons why a hackamore can be worse than a bit.
First the shanks. The shanks give a rider leverage. On a direct rein bit/bitless which attaches at the mouthpiece/nosepiece you are communicating pounds for pounds of pressure. When you have a shank you are amplifying that pressure on two sensitive areas of the horses body. Depending on the shank's length and curve you can be pulling on your horses, nose, poll and pressing on what is referred to as the mental nerve, amplifying many more times the pounds of pressure that you are actually pulling.Which brings me to the next reason; the curb strap or chain. There is a very sensitive nerve under the horses jaw that is part of the trigeminal nerve branch called the mental nerve. The trigeminal nerve branch runs all through the horses face having a few more sensitive nerves stand out from the rest. The mental nerve is one of them. When pressed upon it creates pressure and pain, every time it does not matter if your curb is padded with cloudy memory foam, it's still pressing on the mental nerve. A lot of horses ridden in a curb bit for the first time (a curb bit is any bit that the reins attach lower than the mouthpiece) will toss their heads, shake them and even rear right up. The same can be said about hackamores. This is because of the curb strap on the sensitive nerve. Horses learn they can avoid the pressure or seek it's release by a) tossing their heads as commonly seen with mechanical hackamores b) stopping fast and quick. c) rearing, bucking, headshaking etc.
If you put a rigid noseband with a medium shank or bent shank and the most common type of curb, a chain with leather buckles on each end you are setting your horse up for a painful experience in inexperienced hands. If you should not be riding in a bit with shanks and a curb you should not be riding in a mechanical hackamore. The same pain can come from a "bitless" hackamore as a shanked bit, if not more because a lot of hackamores are commonly misplaced very low on the nose, thinking the lower the noseband the more leverage they will have over the horse. They are right, but the nasal bone is very thin there and it is common knowledge a horses nose can be broken by a mechanical hackamore.
With the right training a mechanical hackamore can be a decent tool but I would say a good majority of people who use them did not take the time to teach their horse to woah off very little rein pressure or flex at the poll when pressure was applied so they are going to have head tossing, a lot of curb chain action and possibly even a hurting horse.
So when searching for a bitless as a kinder, gentler way of communicating with your horse stray away from anything with shanks and a curb chain. I put bitless bridles of the hackamore category with people who resort to the bigger bit because the regular snaffle did not make the horse listen. Time to go back to the training pen and fix why the horse was not light and why we now need something stronger, more severe. Horsemanship should be about communication, not pain. That is what my goal is.