Bullpups marketed in the US have to meet the established OAL requirements.The bullpup is the perfect example of the absurdity go SBR rules, if concealability is really the argument then bullpups wouldn't be legal. Reality is that for now they're just forgotten about by the feds.
My Aug has the same OAL as a pinned 14.5" AR, but it has a 20" barrel so that's the advantage of the bullpup approach.