The concept is that when doing a tactical reload (this is pointless for target shooting) you do the following steps on a normal AR (assuming right handed shooter):
1. Use trigger finger to drop the mag/grab new mag with left hand.
2. Insert mag with left hand.
3. Hit bolt release with left hand.
4. Reacquire hold and fire.
The BAD Lever enhances this process by allowing the bolt release to be tripped by the trigger finger while you are reacquiring your hold. Saves a little bit of time, but feels significantly faster. Here is Magpuls link: http://store.magpul.com/product/MAG980/100
Installation takes 2 minutes. No modifications are required. It simply clamps over the existing bolt catch/release and is aluminium like the receiver (finish is identical too). One screw and you're done. I highly recommend it for any tactical AR. I picked mine up at Sharpshooters for $29.99. Pricing is more or less the same everywhere.
Edit: Forgot the pics. You can see the WC TTU in there. Dark grey finish, wide and smooth trigger face.
