http://ecx.images-amazon.com/images/...3L._AA300_.jpg regular kimberwick with a low port
Kimberwick uxeter with a french link
Generally, remember that the smaller the mouthpiece, the more severe a bit is. A leverage bit(kimberwick, pelham) vs a snaffle is going to have a lot more power over the snaffle. The further away from the mouth the reins hook up, the more leverage you're going to have. Necessarily, leverage isn't a bad thing. Some horses just don't do great with it. IMO, I'd never use a tiny twisted mouthpiece, I just don't like them, think they're too rough. Other horses naturally do better in a snaffle.
If you're serious about equitation, I wouldn't work with a regular kimberwick. Reason being is, any english rider/jumper needs to feel the corners of the horses mouth. As someone stated above, it you have the feeling that chain that runs under the horse's mouth is going to be too much.
I don't like gag bits either. If your friend isn't a trainer or something HIGHLY experienced with horses, wouldn't suggest it.
Different mouthpieces are going to have different effects on your horse's mouth.
For example, a plain old broken mouthpiece is going to to have a v pull on your horses mouth. It's a good idea to use bits outside of the horses mouth and look at where the pressure is put, and what kind of shape the mouthpiece creates.
The french link mouthpiece is double jointed so it conforms more to the horse's mouth. It has a u-shaped pull on the horses mouth. Are you following?
That's a baucher snaffle. It doesn't have a curb chain like a pelham or plain kimberwick does. I'm sure you could get a slow twist on it if you desired. The baucher snaffle has a tiny bit of leverage to it so it may just work.