Well, it depends on your usage and the knives you use. If your knives are cheap and you don't use them often, then we recommend a 2-stage knife sharpener. But if you have expensive knife sets, we recommend buying the 3-stage sharpener get the best sharpening result every time. You might find one-stage sharpeners, but most of them are not so efficient and will give you a rough-to-the-touch and blunt knife, so we usually don't recommend that type of sharpeners. If you already have a one-stage knives sharpener, we don’t recommend using it with a serrated knife, otherwise, it will give you a damaged knife beyond repair.