I've had a CO2 discharger in my shooting/range box for about 5 years or so. They work great on percussion. With the flint adapter, they are much less useful...if you dry load a ball in a flinter, it will usually be driven down enough to cover the vent hole, meaning the adapter can't get in behind the ball. If you can work the ball forward a bit, you can get it in, but then you can probably get in enough powder to blow the ball out. The discharger does work if you bring a loaded gun out of the woods and need to unload it...because then the powder in front of the vent hole gives enough room for the gas to get behind the ball.
A warning: I left my discharger out on a bench at our range after blowing a ball out for a shooter....it was August, and the sun heated it enough for the CO2 cylinder to blow up and blow up the discharger....One more point, if you are going to try and use a discharger, it is better to do it before you try and pull the ball with a worm,,,the worm will spread the ball and make it fit tighter...Hank