Maura, It seems like you may be confusing the chambon with something else- as the only thing that it does encourage is low and stretched forward :p
Personally, I find them to be one of the best pieces of equipment i've ever invested in.
I love lungeing- I think it is super useful for horses, they get to work without any disturbances on their back. So, for equipment, I find:
Pessoa- No thank you, I find that horses go behind the vertical and generally disengage in it.
De gouge(Only mentioned because I alllwayys confused de gouge with chambon) Also not a favourite of mine because it too, can encourage horses to creep behind the vertical.
Chambon encourages stretching down and forward, which is what you want (well what I want anyways :p)
Chambon- see how the horse stretches out and forward, while still being low enough to encourage the back to come up and those muscles to work! :)
Au contraire, here is a de gouge- see how the horse is encouraged to bring the nose to the chest (or rather just unable to poke his nose out)
Similarly, the pessoa- but added in that the movement of the back legs can jar the horse in the mouth :)
Of course, all these systems are (like everything else in the horse world) fine when used properly. I'm just very very picky about my horses going behind the vertical or anything of the kind, and therefore the chambon is the best system for me, and I hiiiighly reccomend it. Sustainable dressage also has a great article comparing these systems :) (Disclaimer- none of these pictures are mine!)