I have used only two in the past forty years. The first went on a 20 gauge fowling piece and it was a tremendous lock. It sparks like a cutting torch.
The second is a lock I bought through this web site. It didn't spark when I received it, and I thought it was the mainspring that was too weak. So I took it to Dixon's GM Fair in 2007 and showed it to the Davis rep there. He took the mainspring out of his display lock and it was better but still not what I expect from a flintlock. I attempted rehardening the frizzen several times and made only small progress. So I sent the lock to Bob Roller who completely rebuilt the guts. Now the action is much better, but it still didn't spark worth putting on a gun.
In desperation, I sent it to Larry Zorne at the Mold and Gun Shop, and he replaced the frizzen. It now sparks fairly well, but I'm still not particularly enthusiastic about this lock. I love the plate, cock and frizzen, but it is not a good lock. I might put it on a blunderbuss....