If you don' shoot enough to burn a pound, the little bit of extra cleanup should be no big deal.
Pyrodex and 777 used in a flintlock require a small amount of FFFF in the barrel under the main charge to ensure proper ignition, per Hodgdon. One more reason to just use BP.
Pyrodex has a pretty good reputation for stability, if stored properly in the original container.
BP just lasts. I've had no trouble with year-old quickloads or powder kept in a good flask. I would never trust 777 that had been open for even a year except for practice.
