What develops a top line is the horse 'carrying out to the hand'...the horse being up/open/lightly in front of the vertical/and in balance/steadily forward.
A chambon might have a purpose of lifting the bit in the horse's mouth, this causes the horse to chew and extend the neck out and forward. Used in this way it is meant to be combined with work in hand (teaching a half halt/mobilizeing the jaw/lateral flexibility/etc)...which almost no one would uses a chambon does. But it has the downside of easily putting the horse onto the forehand. And if the progression of work in hand is not used with this, it has little use ridden.
A degogue limit the height and openness of the throat latch and tends to pose the horse too closed and low. It easily tenses the back and is not kind to the bars.
Both, esp the later, can easily create a horse which is trapped, and can flip over. In short both address the neck of the horse, and rarely the entire body (and even then only specific cases)
A better solution: correct riding, using figures, timing the aids, creating a horse which is up/open/active and which will easily chew the reins from the hand and legnthnen the outline.