I can't speak to the quality of the Lyman Trade Rifle. I've never handled one. I have a Lyman Plains Pistol, and for the money, it is a good value.
As for authenticity, Lyman's trade rifle leaves a lot to be desired. I think (my opinion only) that Lyman took a look at the half-stock Leman Trade Rifle made by Green River Rifle Works back in the seventies, and developed a visually similar rifle modified to so as to be compatible with mass production techniques. They then put a flintlock on it and pretty much invented the half-stock flintlock trade rifle.
In no way am I putting this rifle down, or the people who buy and shoot them. I'm sure it is a good, solid performer, like the Plains Pistol, and superficially it looks very traditional. It should be fine for all practical purposes. It's just that it is not a copy of any sort of original, and under scrutiny, you find subtle non-traditional features.
As far as I know, flintlock
trade rifles, meaning those intended for the Indian trade, were universally fullstocks. There were certainly some half-stocked trade and treaty rifles, but
as far as I know these were percussion. This is not to say half-stocked flintlocks did not exist. This illustration was drawn by Peter Rindisbacher, a young Swiss fellow and a professional artist, who lived at the Red River Colony in Canada for a short time in the 1820's:
I believe that is a self-portrait, and the firearm is likely a smoothbore, but it is unquestionably a half-stocked flinter.
There were half-stocked flintlock rifles, too. This one is from Texas, made by a German immigrant named Erichson:
That image came from Chris Hirsch's "Texas Gun Trade" website.
This next one may get you even closer to what you're looking for, although it is also a smoothbore. It is now, anyway... We wonder if it might have been bored out at some point. It is an original halfstock made by John Derr:
The Derr rifle was recently up for auction, and is from
The Collection of Steve & Marcie Hench. The seller indicates it was "...perhaps made for a local Native American," based on the embellishments. I don't see anything about this rifle that necessarily says "Indian" to me, but who knows? In any event, this looks like a very nice firearm, made by an established gunsmith. It is not a common trade rifle.
So, when you get your Lyman Trade Rifle, I sincerely hope you use it and enjoy it, and I doubt anybody but the most nit-picky of reenactors would give you a hard time. If he does, just point out his chrome-tanned moccasins or Hong-Kong readymade beadwork or farby neck-knife with the coyote jaw handle and be on your way. However, if you take a serious interest in trade guns, and want something closer to the originals, there are some professional builders, as well as some good quality kits, that should get you there.
Best regards,
Notchy Bob