...This has really nothing to do with the discussion on Tom Thumb bits, and other shanked snaffles. I cannot see the connection.
It has quite a bit! As I've explained, I've used Tom Thumb bits and cannot get it to act remotely like that Mark Rashid claims! When I pull on the reins to the inside, the entire Tom Thumb bit slides that way. I have direct reined a horse at least a thousand times in a Tom Thumb, and my horse behaves fine - both Mia and Bandit. Neither had ever been ridden in a curb bit before I started them in one. I used a Tom Thumb bit for Bandit's second ride in a curb - and he did fine!
Why? Two reasons. First, I taught him (from the ground) how to get release, and then GAVE him release. Second, I never tried using the bit in a way it wasn't intended. DO those things and a Tom Thumb bit will work just fine.
Use it to manhandle a horse (Clinton Anderson flexing a horse nose to knee), or use it without teaching the horse how to get release, or use it without ever giving release (Clinton Anderson flexing a horse nose to knee), and it will be a harsher bit. Although it will still be less harsh, by design, than this well respected western bit:
A Jr Cow Horse will pivot at the mouthpiece at the slightest pressure. It will very easily twist the top of the shank into the horse's face. It is almost as straight as a Tom Thumb and has a thinner mouthpiece to increase the PSI on the tongue and bars. The same leverage.
Yet I owned one and used it off & on for several years without problem. Many people swear by this bit. But the people who buy one are typically people who know how to use
one - unlike the Tom Thumb.
"It's just really hard to transmit a really soft and clear signal when there is rotation AND direct pull, AND curb action happending
No. It isn't. NOT IF THE HORSE IS TAUGHT. Horses are not engineers. They do not break things down into each individual component, then try to figure out what each component is asking, and then try to resolve the differences. THAT is a human approach. Horses just memorize the overall feel. "If I feel these 12 things at once, what should I do?
Consider this picture where I'm asking Bandit to do a tight 180 in a solid shank curb bit:
When I applied pressure to his neck, I told him to turn. Tight, since I've applied more pressure than normal. So far, good. But the solid shank curb has rotated in his mouth, telling him to stop quickly! It has also pulled and twisted in the mouth, applying pressure against the inside of his face, which means turn the opposite direction! What is the poor horse to do?
Well, he's doing it. Making a tight 180 turn to the left. He has felt all those things before and is giving himself relief - by listening to the neck pressure and ignoring the rest. Or more accurately, by feeling all the rest and still knowing how to get relief. He's a horse. He hasn't broken it down.
There was no one to take pictures when I rode him today in the same solid shank curb. I used one hand part of the time. I direct reined some of the time. According to all the books, Bandit should have been confused or panicked when I used both hands. But Bandit hasn't read the books. I've direct reined with him before, in the arena, using the same bit. I also showed him, from the ground a la Warwick Schiller, to flex laterally when two hands are used with the solid shank curb. And so he did what he was trained to do.
Would I hop on a strange horse and try it? No. Did it take Bandit more than a couple of minutes of ground work to figure it out? No.
Horses notice and accept the totality of what they feel, and respond as they are trained. The problem with the Tom Thumb is that most people who use one skip the training...
Oh...and there are also a lot of horses whose previous owners used a Tom Thumb badly. Those horses will have issues with one
. They do not forget.