Personally I love the idea of the big one-handed gun. That's cuz i love .357 Magnum (and .44) and other similar kick-ass weapons.
But it's still a Small Guns category weapon (like the .44 Magnum we actually can use in FO).
Face it - the only drawback of big gunners is the possibility of having arm crippled and becoming defenseless. One handed BG gun would make big gunners definetly the most powerful concepts in FO (I think they are already, but...)