A Chambon is typically used when longeing (as intended), whereas a De Gogue is more often used under saddle - though it can be fitted for use on the longe as well.
They are often spoken about as being similar, but in reality the actions they have are somewhat opposite. The Chambon encourages the horse to stretch down and out, whereas the de gogue is intended to encourage the horse to raise the neck at the shoulder and elevate the poll - though both come into action when the horse lifts the head above the limit of the tool.
In my experience, I have only actually seen the de gogue used incorrectly - fitted too short and used to achieve a “headset” by riders who do not understand how to bring a horse along from a low, stretchy outline and gradually developing the musculature to be able to lift the shoulder and elevate the poll. It’s sort of a double whammy: the horse is not physically ready/ trained to do what the tool asks, and the rider is not educated enough to develop it properly. I have yet to see a trainer who successfully brings horses to the point where they can lift through the shoulder and elevate the poll consistently actually use a de gogue.
I have used a chambon once in a blue to encourage stretching over the topline on the longe. Again, simply in my experience I have not seen a chambon misused as frequently as the de gogue - though it is just as easy to set it too short (same with side reins, etc.)
Like any tool, both can be used in a way that is helpful to a horse or in a way that is harmful. It is my experience that in the vast majority of the time, they are used out of ignorance/mis-education by folks who see “getting a horse’s head down” as the goal, and who lack an understanding of training and physical development/ the skills to bring a horse to that point.
Another thing to consider is that many tools were developed many years ago. The de gogue was invented sometime in the 40s (I am fairly certain). Viewpoints on the best/kindest/most appropriate methods to bring horses along and develop them keep evolving and changing. A tool that might once have been in the back-pocket of many high-level trainers may no longer be seen as the best route to achieve the purpose it was designed for.