My limited experience with "imported" factory made flintlocks was very motivating. It motivated me to save enough for a custom/semi-custom flintlock.
Being left handed, I bought a Lyman Great Plains flinter, and later an Cabelas flinter. (Both are made by the same maker in Italy.) It took a while for both guns to 'shoot in", having rough bores until broken in. Tore patches all to hell until then. Both fired most of the time, but were hard on flints. I would say that the flintlocks were 75% reliable. I could expect some klatches or flashes from time to time. There are also some issues with the breeching systems.
I also have watched many You Tube shows on Flintlock Hunting and regularly see the hunters have miss-fires (hang fires or klatches) when hunting with factory rifles. The few that are hunting with semi-custom guns seem to have better experiences with reliability.
I now own a few custom or semi-custom lefty flintlocks with either Cochran or Chambers Siler locks (and have owned two with L&R locks). Ignition is instant and consistently reliable. Flints last twenty or more shots (often twice that) and only occasionally need to be touched up to keep shooting. I would say that my flintlocks are now 99% reliable.
All imported flintlocks are not JUNK. Many do enjoy shooting them, and with the right care, can keep them running. For me, there could be no going back.
ADK Bigfoot