Reverso Four wear and tear is normal. I have been using mine for years and it was used most heavily during an IFSC World Cup climbing event two or three years ago. Over the years I have grown in proficiency with the device and I trust it.
The beauty of the Reverso 4 and similar climbing devices lies in the simplicity of use. Pass the rope through, clip the carabiner through and attach it to the harness.
Belaying is a core climbing skill. With good belaying a climber can climb as fast as he is comfortable to climb, as if without a rope and yet have his fall cushioned at be safe at all times. The belayer needs to be active. He needs to observe and be attentive. I first learned to rock climb with a rope about ten years ago on the Italian side of the Alps and at the time I enjoyed climbing more than I enjoyed belaying. I then spent several years climbing via ferrata instead. The advantage with via ferrata is that it’s a simplified form of climbing. 
Over a year ago I started climbing indoors daily as I finally found a group with which to climb. My interests and skill in belaying improved. Yesterday I assisted a short belaying perfection course in anticipation of the Villars IFSC climbing event. During this session we were reminded of a few key points.