This video gives a good demonstration of the Magpul BAD Lever and several other AR-15 accessories.
The Magpul BAD (Battery Assist Device) Lever is designed to considerably improve the speed and efficiency of the AR15/M16 bolt catch. The BAD Leve quickly addresses reloading and malfunction clearance shortcomings of AR15/M16 platforms by extending a paddle to the right side of the weapon, allowing manipulation of the bolt stop from the fire control/ready position with the right-hand trigger finger.