Ceramic knives have a smaller, but stable share of the kitchen knife market. They have a very high hardness of around HRC 75, with the excellent edge retention that comes along with it, but also an extreme brittleness. Due to this brittleness, ceramic knives are usually sharpened at wider edge angles, to avoid chipping in daily use.
As a result, they offer a sharpness that, as compared to a well sharpened steel knife, must be called mediocre. Also, the cutting edge of ceramic knives is not free from wear. If worn, micro-chipping along the edge is a very common occurrence. However, this will produce a micro-serration that to a casual user might feel as a good sharpness, one that will be kept for a very long period of time.
Thus ceramic knives are a good choice for casual users that want a light weight knife that cuts ok and doesn’t need to be resharpened.
Still, they have to be treated carefully - not cutting hard objects, not bending the blade, not dropping the knife, to avoid chipping or breaking.