The text in this review reflects our assessment of belay devices in 2009. The Mad Lock has since been discontinued, but we have updated our review of this gear category multiple times with recent selections. Our latest Belay Device review is right here!
The Mad Lock is one of the most versatile belay devices we tested and one of the lightest devices for belaying off the anchor. It was the smoothest device for belaying two 10mm ropes, simultaneously, in auto-block mode. Essentially, this became our preferred all-around device for use with 10mm ropes or greater in most situations. It works with ropes from 8.4 to 11mm. It had noticeably poor friction control on smaller diameter ropes. It also costs much less than all other auto-block devices tested.
That said, if you use thinner ropes, the Reverso 4 is still the top-scoring device for belaying off the anchor (but costs almost twice as much). Also, we did not see where Mad Rock says you can belay two individuals with this device. The Reverso and ATC Guide do let you belay two followers.