I’ve replaced a bunch of Lott locks over the years. They were made by several companies during that time. Some are junk because who ever made them at that time had almost no quality control. The geometry in these lock is the main problem. This is obvious if when you put the cock at half cock without a flint in it, the cock is obviously too close to the frizzen. The main springs are almost always over polished, and over tempered, making them weak. Lott lock other than the one with the obvious geometry problems can usually be made into a serviceable lock by either retempering the main spring, and either half soling the frizzen, or case hardening it.
I have two of these locks on my bench right now. Both of them were off of the old Green River Forge trade guns and have had the “Lott” ground off and a sitting fox engraved in its place. One has been shot so much that the frizzen has been grown flat and rehardened so many times that the edges of the frizzen are as sharp as a knife. It’s obviously time to half sole that one, and depending on how well that goes, maybe the other one as well. The internals on both these lock are in fine shape, so they are NOT junk locks in my opinion.