Here's what other sites are saying:
Fixe's Faders Sum Belay Device is safe, for all your sport-climbing ropes, resistant, ergonomic, dynamic, light and easy to use! Sum is a new generation belay device/descender designed to belay the first and the second in sport-climbing routes or climbing-walls. You can give rope fast and easy without touching the lever.
The SUM belay device is a new generation of belay devices designed to auto-lock when belaying a lead or top rope fall. The SUM is designed to safely belay and repel on the most popular rope diameters The SUM is specifically engineered to pick up where its competition leaves off. Ropes in the 9.1 - 10.5mm range can now be safely handled using the SUM. Thanks to its ergonomic and intuitive design, the SUM is not only safe and strong, but also easy to use. It operates smoothly and efficiently while paying out rope or taking up slack. The SUM quickly auto locks in the event of a fall
- Vargo Outdoors