The Busa has a back torque limiter which is sorta like a slipper clutch, but not as effective as aftermarket slipper clutches.
If you downshift into high rpms when heavy on the brakes, aftermarket slipper clutches are a big help to keep the bike stable. But they are not cheap.
Honestly you don't need one for street use. But if you do trackdays and have the money, its worth it.