I interpreted the OP's question question to be whether we prefer priming our flintlocks from a priming flask or horn.
A lot of shooters now say we ought to prime from the same horn that carries powder for the main charge, because that's how they did it back in the day. I'm reluctant to open that can of worms again, but will respectfully suggest that we do a lot of things differently now. Coarser powder, even FFg, will light up just fine when sparks fall into it, but for me, FFFFg seems to be a little faster. Not that I'm a good enough shot to benefit. My main problem in priming from the "big" horn is that I am clumsy, and usually end up putting in too much powder and/or scattering powder all around the pan, into all the little crevices and around the feather spring. Getting off a shot becomes a pyrotechnic event.
I get best results with one of the little tubular brass priming flasks with the small nozzle and spring loaded valve. I fill it with FFFFg.
That's what works best for me. Others March to their own drummers.
Best regards,
Notchy Bob