Leman is known as one of the suppliers for trade guns the Government's supplied to the Indians however, the company, in Lancaster, Pennsylvania made a large number of rifles sold to the public.
Actually, the company goes back to 1730 when Hienreich Leman established it.
The rifle you are considering is fairly typical of the guns made by them in the 1820-1840 period so both flintlock and percussion locks would have been offered.
The guns were intentionally designed and built as a lower cost working rifle. For that reason they often were made with plain maple stocks and for a few dollars more, they would paint stripes on the wood to make it look somewhat like it had a more costly, curly maple stock. (This is one of the few times I've heard of where a company actually painted fake stripes onto a stock.)
Although the Leman rifles never received the literary "hype" given to the Hawken, I have no doubts that many of them were carried into the Western mountains by fur trappers.
If you have some talent working with wood and metal, you might consider buying one of the TVM "kits". The Leman is usually considered to be the easiest "custom" kits.
A word of warning about these though. They are not the easy to do, almost "fall together" kits like you might get from Traditions or Pedersoli which one can finish with 15-30 hours work.
All of the pieces except for the lock and barrel are basically rough castings and a rough shaped stock. You would have to not only finish the parts but you would have to locate, drill and tap all of the screw holes to hold everything together.
Typically, one of these kits will take over 100 hours of your time.
You should look around in our "Gun Builders Bench" to get a good idea of what is involved.
I didn't see that they were offering their "in the white" builds on this rifle but TVM offers many of their rifles in this condition.
A "In the white" gun supplied by them is fully assembled but the stock and steel parts need to have a suitable finish applied to them.
With the stock this would consist of some finish sanding, staining and applying a suitable gun finish ranging from linseed oil to Birchwood Casey Tru-Oil or Tung oil.
If you think a "In the white" gun might suit you, call TVM and ask them if it is available.
That could save you several hundred dollars.
Whichever route you take, I'm sure you will be very happy with your new Leman.