Here is what I've been trying with Mia. We went off property & around the block today with it for the first time. Each shank can move about 45 deg independently, and then the other shank will move with it. Each shank can swivel out independently. The middle doesn't bend, so there is no nutcracker action.
I did some ground leading with her first, but I guess I never pulled back enough to engage the curb strap. The first time I did that, on her back, she flung her head up in surprise...so we did some more ground work so she could get used to the progression: bit, then poll pressure, then curb strap engaging.
Based on 8-9 rides, I'd say she probably does a little better with neck reining using this than with a snaffle, but I don't think the difference is huge. On the plus side, she seems to instinctively take pressure on the poll to mean "Bring your head down and slow", so she seems to respond to bits that apply poll pressure faster and more willingly than with a simple snaffle.
It is still easy to direct rein with this. On our first ride off-property today, we reached a spot in the neighborhood where the wind was blowing, dogs on three sides were barking, a guy was using power tools on his car, and another guy was spraying his yard. That was too much for Mia. She stopped and gave a little prance, and I pulled her head about 90 deg left by bringing the left rein out and slightly back. She gave me her "I'm scared" look, so I told my daughter on Trooper to take the lead. Mia then stood still while I scratched her neck. As Trooper passed her, she sighed and walked on.
I'm pretty sure the direct rein pulling didn't hurt her, because she relaxed right away and acted at ease for the remaining 10 minutes of riding, including a short canter. She also acted like a big affectionate baby after the ride, so I know she wasn't offended by anything. She is enough of a princess to act offended if she thinks I did something unfair during a ride...
I haven't tried a pulley stop with this bit, and I'm not sure I would. I'm guessing here, but it seems to me that would apply way too much pressure. It seems like a bit to use by applying steadily increasing pressure over a couple of seconds, so the horse can choose to respond. If your horse didn't stop with one hand using this bit, you probably have problems!
Right now, I'm thinking this may be the bit that Mia & I need to work well together. Of course, it will take a lot more rides to be sure. It is based on less than a dozen rides on one horse, so take it with a big steaming cup of FWIW!