Here's what other sites are saying:
Born as an emergency rope clamp for retrievals, progression maneuvers and daisy-chain regulation, the KONG USA Duck Multiuse rope clamp works with ropes and both flat and tubular slings.
Kong Ascenders & Descenders Duck Rope Clamp/ascender 888. Simplicity and function. The Duck is a rope clamp ascender that completely surrounds the rope or webbing for safety. The outside radius of the carabiner hole provides a predictable surface for consistent performance on rope as well as webbing for climbing and work positioning.
Kongo's Duck is a micro-sized ascender developed for emergencies on mountaineering missions. If the topo doesn't recommend an ascender, or you're planning to free the entire climb, then the Duck will be a better option than larger ascenders just in case you have to set up rope rescues or skip a couple difficult pitches.
An emergency belay device compatible with single ropes and slings, the Kong USA Duck ascender is a superlight and easy way to be prepared for self-belay, rescue, progression maneuvers, or daisy chain regulation.This product will be shipped directly from Kong USA and will leave their warehouse in 2-3 business days. Eligible for UPS ground shipping only.. . . Made of lightweight aluminum alloy. Accommodates ropes 8-13 mm in diameter, or slings 10-15 mm wide. Small size allows for easy, one-handed installation on the rope. Large hole accommodates any locking carabiner. Certified EN 567:97; conforms to UIAA standards. Every piece of Kong USA gear is tested and checked for safety.