They are powered by a pistol primer and are designed to fire a plastic projectile, but I carry them with just the primer.
To me, this seems to combine the best of all the options.
1. Because they are empty and plastic, they weigh almost nothing so I can carry a full mag.
2. If you shoot them in low light conditions, they make and awesome flame blossom that will leave the person you shoot them at speechless for at least 30 minutes
(Don't ask me how I know this!)3. Because they are not powerful enough to cycle the slide, I get to make that cool racking sound 9 times before I have to reload. If the flame blossom doesn't get them, the racking sound will.