Pull-through knife sharpeners are a good tool for your cheaper knives and can help to get a slightly sharper edge quickly and safely with little technique required. However, they are prone to degrading the quality of your knife over time. These small tools pull away more metal than a whetstone, weakening the durability of the knife and meaning you have to replace it more quickly. As a result, they may not be the best thing to use with high-quality knives that you have spent good money on.