A house brand is when a store purchases or contracts a line of saxes to put their stores name on. Generally they are pretty good, but not GREAT and not at the level of the big guys. Usually they are sold at a substantially lower price than the big guys so they are an attractive option as a backup horn or even a primary.
From what I have gathered about the antigua sops, the sops they are modeled after are better saxes, but maybe not $X,XXX better.