with the exception of the huge bowling ball mortar that Hern makes, I believe they are all made with a seemless liner with a welded breech plate on the liner, which is then cast around with cast iron to form the finished product. You should e-mail Joel at Hern Iron Works about the specific barrel you have in mind.
I have a Hern Coehorn. I have only fired it a few times, and have had no issues with it to date. The liner is very well centered, and I can not see any problems from what I can see with my eyes. . I have not x-rayed the barrel, so I cannot tell you one way or the other about what I can't see.
The Hern barrels tend to be substantially sub-bored as conpaired to a tradional nore size, so the bore to wall thickness ratio is generally very substantial. I don't recall the specifics of the barrel you are talking about, but Hern uses 2.25 inch ID, 1/2 inch thick seemless liners for lots of their pieces
For what it is worth, I would think that the cast 90# Coehorn barrel is easier to not screw up that a 300-500 pound barrel. That being the case, a review of the barrel you are specifically looking for would be worth waiting for.
There are discussions about Hern barrels on this forum. You will find many debates about cast-in-place liners verses bored barrles with pressed-in-place liners.
However, I don't recall anyone mentioning a bad personal experience with a Hern barrel.