This is a good quality part, but buyers should be aware that it is a metric 48p set of pinions. These will work very well on most (but not all) tamiya cars, but non-tamiya cars probably won't work with these. For most other makes you'll need a standard 48p, not these metric ones.
The durability of these parts is fine, not brilliant. They are light weight, but their lightness also means they wear out sooner and get chewed up easier with small stones getting in them. Even with a sealed drivetrain they will get dirty and it does chew the parts up.
One thing I like about the Tamiya pinions, their quality control is consistent. I've had other gears, including a popular American brand, and 2 pinions were identical, yet the shaft hole size in one was slightly smaller. One pinion goes on a motor just right, the other pinion is extremely tight. YOU NEVER GET THAT WITH TAMIYA PINIONS - QUALITY CONTROL IS FAR GREATER.