Also, if a bit has shanks, without a curb chain...do you have to neck rein with it?
What is the point of a shanked bit without the curb chain? The curb chain is what gives it something to leverage against. The curb chain keeps it from rotating more than about 45° and keeps it stationary so that as you pull the reins, pressure is applied to the chin, bars, tongue, etc. Without the curb chain, the bit is free to rotate as far as you can pull the reins - Nothing to keep it from clanking into the teeth. Shanked bts need the curb chains or straps to work the way they're designed to work. Even the Kimberwick has a curb chain. So to answer your question, don't direct-rein a shanked bit without the curb-chain. If you have to ride one without the chain, neck-rein so you're not really using the bit. Actually, if you have to ride one without the chain, you might be better off riding in a halter...
The Kimberwick is a mild leverage bit, not a snaffle. It does have the advantage of being able to choose how much leverage you want.
The shanks will apply a little more pressure. So a snaffle, with the rings, will apply one pound of pressure on the mouth for every one pound you pull on the reins. So, a 1:1 ratio. A shank bit like that will give you a little more leverage. So let's say it's a 5 inch shank. For every pounce you pull on the reins, the horse will feel five pounds on his mouth. That's why western riders show on a loose rein because it's less pressure to get the same results. It's not a harsh bit really, just a little bit more than a regular snaffle.
You can use it without the chin strap but I'd recommend it just in case, doesn't have to be tight. It just adds a little touch more power plus keeps the shanks a little bit more balanced.
A double-jointed snaffle is actually milder than a single-jointed snaffle. The pressure is distributed to more areas of the mouth and dispersed.
The hanging-cheek aka baucher bit you are looking at would actually be milder than a single-jointed snaffle. Despite its appearances, the hanging cheek works no differently than a regular snaffle.
There is no leverage on the bit so it basically works the same as a simple snaffle. It is possible that there is a very slight amount of pressure on the poll, but not enough to affect the horse.
The Kimberwicke, on the other hand, would be a small step up from a simple snaffle. It has slight leverage, and is like using a curb bit with a very short shank. Because the shank is so short, it does not have the difficulty of instability in the mouth and mixed signals to the horse that other jointed shanked bits can have.
Which brings me to the other bit with the shanks. With a curb strap on this type of bit, there is a lot of leverage so it cannot be ridden in with constant contact (best used with neck reining). Without a curb strap, the bit will rotate around uselessly, pulling the bridle out of place and sending unclear signals to different areas of the mouth.
A good reason to use a Kimberwicke is on a horse that is well-behaved and can be ridden lightly most of the time but on occasion needs the stronger signal of a mild curb to get the horse's attention.
I just received a Kimberwicke in the mail a couple of days ago. I've put it on Mia once and walked along beside her and watched the bit & her when asking for a stop with the reins (couldn't try turns, since she will go where I go regardless).
On the mildest setting, it is still definitely a curb. Mild, but a curb. I bought one with a solid mouthpiece. Interestingly, she acted a bit freaked out when I went to put it in her mouth. And she responded very quickly to very light pressure. Before I owned her, she was sold to a girl for about 4 months prior to being returned, which was when I bought her. I'm wondering if they decided to fix her brakes (or lack thereof) with a strong curb. That might explain why she was so sensitive about her ears when I got her, too! If Mia was actually an unbroke horse at that point, as the trainer I hired last year concluded, then slapping a strong curb on and pulling hard would NOT be a good way to teach a stop!
We spent about 20 minutes walking around with quite a few stops and backups. She seemed much more relaxed at the end, and I then took the bit out and put it back in a few times without her fussing. I plan to ride her in a few hours, but since I'll be all by my lonesome I'll use her normal snaffle for riding today. Maybe put the Kimberwicke in & out a couple of times and do some more ground walking with it.
The longer I'm around horses, the more I believe in taking lots of baby steps in training!
Freia....what would make you decide if you would need to use a leverage bit like the Kimberwick?
Trial and error, pretty much! Different horses like and respond better to different bits.
I'm assuming you direct-rein. This is how I decide. I start a horse I'm not familiar with in the mildest bit: a french-link snaffle. If he's happy and responds well, I keep it. If not happy or poor response, I try a few different things. One horse thought the french-link was too busy, so I tried a single-joint (he has a large mouth with plenty of room) and he's been very happy and responsive. One (very hot - we call her "saucy") horse completely ignored the french-link, then blew right through a single-joint, so I tried a low-port Kimberwick to see what she would do with a little leverage and curb-chain to pull against, and voila, happy as a clam and under control.