The Mammut Smart is one of the lightest and lowest priced assisted-locking belay devices on the market. It is low profile, has a simple design and worked especially well for toproping. We also liked it for belaying the leader, but many testers would repeatedly short-rope us during clips.
The Smart is a great value for an auto-locking belay device. The $30 price is less than one-third the cost of a Petzl GriGri and half the cost of the Trango Cinch. Its also one-fifth the weight of those two devices. The Smart takes some getting used to and we found many people had a hard time feeding rope fast to a leader. However, once we got the hang of it, it worked fine on ropes down to 8.9mm and up to 10.5mm a range the Trango Cinch and Petzl GriGri are officially not recommended for. Like any device, the Smart can be mastered for smooth belaying/rappelling, but it takes more work to get used to than other products reviewed. The Cinch and GriGri still handle better. But the Smart is a great value option and we loved the lightweight package.