I have a Chambers late Ketland and a Dale Johnson Siler on my bench and they, along with one of Bob Roller's, are truly the nicest funcitioning locks "out of the box" that I have ever had. Just literally nothing that seems to be needed to be tuned on them, other than modifying the plates, etc. a tad for my specific projects.
Most of the late English flint locks being offered today are a bit fancier than you see on mountain rifles, but they are close. It is interesting - you don't see many built with the Roller locks, but if you look at some of the photos in Dennis Glazener's book, the Roller lock is almost dead on to several shown on some of the flint Gillespie rifles, and some East Tennessee guns in Jerry Noble's books. Now that the price of other locks is creeping up there, Bob's prices are not that far off from the others now.
That being said, there are some others available. The Davis late Ketland (formerly Ron Long), with the square tail, is an appropriate style and the ones I have picked up at Tim's booth at Friendship seem to be nice. Also, Tip Curtis offers 4 variations on a Late English style - I think Pete Allan designed them(?) (sorry if I am mistaken on that) - gooseneck cock, reinforced cock (like the Roller), bridled pan, "V" shaped pan, in all possible combinations. His are a little bigger than the Roller lock.
I have an L&R Manton on the first Tennessee rifle I built about 15 years ago - it works fine - it eats flints a little faster than my other locks, but nothing severe. I think it did have a screw that was stripped when I got it but any problems I have had with L&R locks they took care of right away no questions asked. I have not checked out any of their locks in a number of years though.
Guy