The idea behind a bullpup is to have a smaller rifle without sacrificing barrel length or ergonomic grip. By moving the action back into the buttstock you reduce the overall length of the rifle but you don't have to cut the barrel down to do it. This means that in theory the rifle would be more effective in close quarters situations. It also means it is less clumsy when hanging on a sling say during a transition to pistol. It does mean relearning the ergonomic considerations of a new platform and getting used to the controls in places you may not be used to.