Don't know anything at all about 'endostick' except for skimming your link - thought it was related to the 'endotap' method, which looks rather... dubious to say the least, but it seems to be different & more about pressure points & such, which can be largely sound principles IMO. However, as I said I know next to nothing about it.
While researching positive training methods, aka occulant training, I kept thinking "But what about HORSES?"
I'm guessing you mean 'operant' training, aka behavioural training, which is not only positive. What about horses? Behavioural psychology is about the principles & 'laws' of learning that animals learn/behave by and is sound for all species. Of course each species has different motivations, but we all essentially learn in the same way and the principles of behavioural modification work across the board.
I find it interesting in having trained horses, dogs, cats, chooks... and used the same sort of principles with my kids(they're the hardest beasts to train!), that when learning & talking to others about it, that some people, if only having experienced it on one species sometimes doubt the effectiveness of use with other animals. I've heard dog people say it wouldn't work for horses, horse people say it wouldn't work for dogs, people say it's only effective on wild zoo animals... people using it on mentally disabled patients say it couldn't work on animals, only people...
It made sense that it could work for on the ground, and maybe in the saddle if the trainer knows how to do it properly. But problem horses? No way. There's no possible way someone with a clicker and a sharp mind could get a horse to stop trying to kick you in the face.
Firstly, the clicker is but a handy tool for use in training. It is a 'bridging signal' to help the horse associate behaviour with positive reinforcement(reward). It is by no means necessary though and whatever original, short, sharp signal you choose will become effective. Dolphin trainers tend to use whistles. I tend to just use 'Good!', especially when riding, so I don't have my hands cluttered. As far as problem horses & stopping kicks to the face or such, I think you're looking at it too directly - as if the clicker is the trainer, the Answer or some such. Again the clicker is but a handy tool, as with food treats or such, it's the *principles* you learn & apply that are the important bits. Then you will learn how to modify their behaviour *and attitude* in order to *avoid* the aggression, rather than just reacting to it when it happens. I actually find using 'clicker training' principles especially valuable in working with 'aggressive' or 'rude' horses.
it is still a form of reflexology and it does not teach the horse to listen to the rider and it does not teach the rider to communicate with his horse as a whole being.
Perhaps, like 'clicker training' IT does not train the horse, but it may be a useful tool to help a trainer?