Gag bits work by putting pressure on the poll, bars of the mouth and the tongue. Because of the pressure put on the poll gags can make some horses overbend, not all but some. I've ridden a mare who really overbent in her gag but I've ridden others who went fine in a gag. Both the bits you showed work on poll pressure though I'd take the second one's description with a pinch of salt because no matter how good a bit is it won't collect your horse for you.
ETA: If you want to work her out of a gag then you could always try a hanging cheek snaffle which puts on a little bit of poll pressure.
I swear by my Jr. Cowhorse. I like the 3 piece mouth though, just a personal preference.
I use them as a step up from a snaffle, so if I were you, I'd go down to a loose ring snaffle for a while, until she's nice an soft with that, and then go up into a Jr. Cowhorse just for a little extra refinement
The gag also pulls up on the corner of the mouth. It's debateable whether or not this is a "lifty" bit or whether or not it does the opposite due to the poll presure. I agree with everyone's posts so far. Also, there's a little more warning to the horse because of the slide and poll pressure before you actually hit your horse's mouth all the way. I really like then for that.
I would go ahead and return to a loose ring snaffle for awhile. I don't like wonder bits at all really.
I just purchased a bunch of stuff from a girl that was getting out of horses. It was a great deal and the barrel saddle is brand new. The western ss copper moon bit came with it and my horse seems to be much better using this. The guy that had him before used a chain bit and I'm not going to use one of those. Anyhow I'm happy with the results :)
If I use a bit I use my Myler combination bit, it's definitely the best for me because it applies nose and poll pressure before suppressing the tongue. But the best kind of bit I could ever recommend would be no bit, but a hackamore or bosal. My horse is light, supple, responsive with a hackamore, I put metal in his mouth and he tosses his head. I don't blame him either! Haha I'd do the same thing! He listens, but he definitely makes it obvious that I'm not being fair to him. Just remember that with the bosal you don't need steady pressure but instead a "bump bump" pull when starting out. If you do any kind of ground work with him, you are working with the halter, same effect but instead you are sitting on him. Only makes sense to keep the metal out of his mouth. Posted via Mobile Device