I have two of the brass plunger type primers. one larger than the other, and I am quite satisfied with them, but prefer the larger. I don't like to carry it in a pocket because I wind up with a pocket tainted with priming powder, which should instead be in the tube.
I don't know the history of these priming devices, but I'm pretty sure they aren't a "back in the day" device. Thus I don't feel bad carrying it as I'm about to describe:I bought a keyring on a retractable, spring-loaded device. Think like a custodian might use to carry a dozen keys. It won't work with a bunch of weight, as it would be heavier than the spring can withstand. On the split ring I have three items, the primer, a vent pick, and a strip of cotton cloth for wiping the pan and frizzen. This is clipped onto my left side on my belt (I shoot left handed).
On the shooting line, in a woodswalk, or while shooting Running Boar I have the tools I need to manage my lock for each shot. And it retracts out of the way after I have primed. I usually shoot in a t-shirt or in a long hunters style shirt, so that places a layer of fabric between any sparks and the primer. (As well as a too-substantial belly between the lock and the primer).