I only briefly looked.. what is the difference between the "C10" and the "G10" lowers ?
And in case you didn't know, there is no "Mil-Spec" guideline for Large Frame AR's... so they tend to be pretty all over the place when it comes to various manufacturers parts fitting another manufacturers product. Even within the dominate 2 patterns. ( DPMS and Armalite... and there are more )
In other words it is no where near as easy as a AR15 when it comes to anyone's parts working together.
And they sure do throw around a lot of "he said, she said" terms for their Large Frame AR lowers.
That said... New Frontier Armory has been around a long time, so they must be doing something right.
Again, just remember the parts issues... it is widely accepted that you want to buy the LPK's and a upper from the same manufacturer.