My Box Gun is going to be considerably less bulky and less boxy than the traditional setup, as well as borrowing some of the design elements of the Duck. It is done now and should be shipping out soon so I will be posting a nice review.
Barrel kits are also now standard on all of his scratch build guns minus the Duck (three different inserts).
And I also got the impression from him is that he does not like slam changers, for the reason Emert has mentioned. He also considers both slam changers and in-handle changers to not be practical for play. His words (through Lauren) were "in-handle or slam changers make great collectors items, but get a BBA for serious playing".