KTM has it right, there are many variables to getting a good burning stove or boiler. When burning Anthracite you can just about throw out the coal quality variable. Anthracite is very consistant quality. However with Bituminous, the major factor is fuel quality. Technique makes up for firebox design problems, but unless the firebox is designed for Anthracite coal first and wood/bituminous second, it will always be a compromise.
With all the issues I've had with Bituminous, I'm amazed that the US stove burns bituminous well at all. I basicly copied the firebox design of my old MBW boiler, and later saw a US Stove boiler at a TSC store and was amused to see the same design in the firebox. I wouldn't have been so amused if I had realized at that time what a compromise that desgn is.
I think that the US Stove firebox is good for wood, and for adding a load of bituminous on the wood for an occasional longer burn, but it is not good for a long burn with anthracite.
In order to get anthracite to burn well in my boiler, I had to modify my firebox with the help and suggestions from several forum members. I have finally got it so that I can burn anthracite well with 12 hour burns.
With the un modified firebox, [US Stove type design] I can just barely get 8 hours, and have less control over heat output.
KTM's AHS boiler is designed as an anthracite boiler first, with a few features added to make it burn wood and Bituminous. The US stove is the opposite, a wood stove/boiler first, with few add on features that make burning Anthracite possible but a struggle.
I'm sure you will be much happier with your Hitzer 82FA, it looks like a good unit. Take a good look at hte firebox, and take a photo or two, then post those photos with photos of the US Stove firebox, so we can see the difference.
The US stove is a shallow depth, long and wide firebox with tapered firebrick sides down to a center grate. The Hitzer will have very deep box with vertical or near vertical firebrick sides with a grate covering the entire bottom of the firebox. I'm describing the Hitzer firebox sight-unseen, just based on what a correct anthracite burning firebox looks like.