Although the lock is "plain", like the rest of the rifle, its function and reliability (on my rifle at least) is excellent. In some respects, I can't figure out why Dixie discontinued the model, since it was probably the best value for a good, accurate traditional flintlock rifle on the market. Actually, I suspect the primary reason was that the ultra-plain style - despite being very "historically correct" - just didn't appeal to enough customers. The majority of the market seem to gravitate to the varnished, brass-mounted Italian "replicas" (most of which don't realistically represent any original firearm type) - if they aren't falling for one of those godawful modern inline models, that is ....
My Tennessee Mountain Rifle consistently held its own against all comers - including "custom" hand-made flinters - in any competitions I shot in. (I only use the past tense because I quit shooting my muzzle loaders several years ago, when I moved on to cowboy action as my "active" shooting sport. I've disposed of quite a few of the front-stuffers I had, but this is one I chose to keep.)
Another great feature of this rifle is the availability - at quite modest cost - of the percussion lock (with drum & nipple) conversion system ... which is essentially the same as the method originally used to convert flintlocks to the "newfangled" percussion system. With that addition, you have two rifles in one!
Happen to have a composite picture of my TMR handy, showing both ignition systems. (I didn't like the overly reddish tone of the original stock finish, so I redid it, and also installed a plain steel patchbox in place of the "grease hole", which didn't appeal to me ...)