I am fond of the spur stop training. I know Avila is great, and I learn a lot from reading what he writes, but I think he is missing the boat on this. Have you watched a top end reiner? They stop on a loose rein, they don't call it a spur stop, but they quit pushing, sit deep, and freeze their legs and hands, and voila! that beautiful slide. Well not automatically, but after lots of good training. Spur stop is not for every horse in every event, but I know people who run speed events on their spur stop horse, and others who show over fences on their spur stop horse. Riding the brakes is WRONG and leads to problem areas, but using the spur to cue is just another button you can put on your horse.
What do you usually do when you want your horse to stop? This pertains to both english and western riders, but actually, especially english. You kinda "freeze" right? You quit following the horse's motion, you create a "fence" with your hands, and you also wrap your legs around him, and "freeze" your legs. You ride them into the stop so that they do not stop all strung out. A spur stop is EXACTLY the same, except that you do not, since you are riding with a loose rein, pick up the reins. You stop yourself from head to foot, and the horse follows suit. For show purposes, it is refined from this, but this is the principle.
How do you turn your horse? In the simplest terms, you increase pressure with your outside leg in addition to rein cues, right? This is spur trained. "Spur trained" is a concept it does NOT have to use spurs, my horse will perform about the same without spurs, I just use them to reduce my leg movement to touch his sides.
How do you cue for a back? You use your legs there too, right?
How do you cue for a half-halt to slow or collect the horse, you use your legs to push him up into the fence of your hands right? With the western spur trained horse, the "fence" is understood, since contact is not allowed, ones back and seat communicate the fence.
Instead of thinking about the horse blowing, I read another fan of spur stop that stated something like: "what does an experienced rider do when they are frightened that the horse is running off? They try to grip tighter with their legs, and often drop the reins, or grab onto the saddle, and can't pull on the reins....on a spur stop horse, this is cue to stop, where as on a conventionally trained horse, the frightened beginner is telling the horse to go faster." I can't imagine trying to ride bridleless on a not spur trained horse.
"Spur training" is just an extension of what we have always done. 40 years ago, I prided myself on my horses who would back up from the line up with me just picking up on the reins, not and contact, and squeezing them to back, now I don't even have to pick up, no fundamental difference, only a refinement. My old horses always would turn on leg pressure, now they will slow and stop also.
ANYTHING can be over done to the point of abuse. I HATE to see a person who "rides the brake" and only lets the horse go forward a step by relaxing leg pressure, that is just wrong. On my spur broke horse, to whom slow is his natural gait, I have to bump him more than I should (because I have spoiled him) to make him move on! Then I "freeze/squeeze to call for a change in gaits down. To quote another trainer "bump to go, squeeze to slow." Not that backwards to me, given all that I said above.