Designed for wide cracks, the large but sleek design saves on weight and racking space when comapred to large cam devices. They use an expandable tube chock design to protect horrible, scary wide cracks. Just place the Big Bro in the crack, push the button to extend it to the right size and twist the sleeve to lock it in place. Since the Big Bro's resist pull in any direction, they are nearly impossible to accidentally dislodge as you climb. They do need more practice with placing than cams, but once the trick is mastered then they provide a method of protecting otherwise very bold awkard climbs.