My first build was a Tennessee rifle from Pecatonica and I was very happy with it. Dick Greensides was great to deal with and actually will work with you on options - barrels, etc. moreso than their website indicates.
Some of their assemblages of components are better than others with regard to actually looking like the styles they are intended to represent. This is typical of many of the component sets on the market, when existing common available castings and locks are grouped to try to portray a certain "style." So what happens is that you can end up with a triggerguard, triggers etc. that are on the kit because they were the closest thing available that fit, rather than being really correct for that style gun. As others have said, if you are able to do a little more inletting, you can have Peatonica leave things un-inlet and select better choices of locks and hardware for your particular style if the ones offered as standard are not what you want. One example of this is the use of Siler flintlocks on 1830-40 style Tennessee mountain rifles - they are just not really correct. (Although I realize that Pecatonica offers a choice of locks on some of their Tennessee patterns.)
Some suppliers offer castings that were designed just for their kits, or at least carefully selected to ensure that they are completely appropriate - Chambers is one, and there are a few others.
Whatever you go with, have a good idea of what you are trying to portray before you buy. "Kit bashing" from precarve can be a lot of fun-as long as the basic shape is there - you can then customize it as you see fit. There is nothing sacred about the shape of a barrel tang, lockplate (unless these things are already inlet), curve of a triggerguard grip rail etc. "out of the box". Sideplates are pretty easy to make - especially for Tennessee rifles. The key is being able to see that what you select to start from is a good starting point to get you where you want to go through modification.