When vertical caving, I always have two of these clipped to my harness in the event my Basic or Croll decide to call it a day. It's a minimal, lightweight, emergency device that will get you up the rope safely without the hassle of fooling with knots. As mentioned below, this isn't meant to be a primary ascender under any circumstances. Would you use an emergency "space blanket" as your sleeping bag? I still have Prusik loops on hand -- you can never be too safe -- but the Tibloc is my first line of defense.