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.
Years ago when choosing a belay device I was tempted and curious about the Grigri device but at four times the price of the Reverso I thought I would wait until I gained belaying experience. Three years later and this is the state of my Reverso Four
In the image above you can see that the left side is still intact, having almost never been used. This is because as a right handed person I always use the right side. You can see that ropes have worn away at the two front teeth. In the featured image you can see that two of the teeth are worn smooth. I have not noticed a difference in braking ability.
Although I have used this device for lead and top-rope climbing I have also seen it used for rappel by some people when at a climbing gym in Lausanne. If you pass both sides of the rope through the device you are able to control your descent using a single rope. It can also be used for climbing with two ropes.
I have two Reverso 4. The bottom one has been used every time I have been climbing and the top one is almost new, having only been used for climbing a few times. You can see the shape that the teeth should have and the shape these same teeth have after hundreds of metres have rubbed along them.
The reason for which I got a Grigri 2 is not that either of these Reverso 4 replacing. I was not even considering replacing them until a conversation Wednesday night. Someone with more climbing experience was speaking about the safety advantages of the grigri so I decided it was finally worth the investment.
In scuba diving when you upgrade your equipment you can easily spend thousands of francs. In this case it was around 70 CHF for something that lasts for years. Contrast this to diving equipment where you spend hundreds of francs for every new toy. In theory this is a device that I will use at least once a week for several years.
When I gain experience I will write another post.