Review on JASGOOD Canvas Elastic Keeper 1 5Inch Men's Accessories for Belts by Michael Sharp

This is a decent solution to the problem of wavy belts. But they have a limited lifespan: they're basically just a loop of stretchy material that works great the first time you put it on, but over the course of a few weeks it will stretch and lose its support. As they come in a 5 pack for a relatively cheap price it's not too bad, but a more resilient stretch material would be an improvement.