Getting water to flow well through a filter cone is a fine balance. If the surface of the cone is too smooth, there is not enough space between filter paper and cone for the liquid to flow. If the surface is too uneven, water will form into drops between the paper filter and cone and flow will be slow. Somewhere in between is the perfect balance - a slightly uneven surface that allows a quick flow of liquid in the narrow gap between filter paper and cone.
These porcelain 1x2 size filter cones seem to have that balance. I have owned a couple of plastic cones, made by Randwyck of Maastricht, for many years. Those, like most plastic cones, are heavily ridged inside. These porcelain cones, as can be seen from the product photograph, have slight ridging inside which works very well. Liquid drains through these porcelain cones much faster than through the plastic ones. I estimate that making a large mug of coffee, I can fill the mug through this heavy porcelain filter cone in half the time it took with a plastic one, where flow slowed to a trickle as the mug filled.
The cones are of a substantial piece of porcelain and are made by the established manufacturer William Bartleet and Sons. Compared to plastic cones, the porcelain is very easy to keep clean.
End result, a lovely mug of coffee, quickly made. Unless you have a particular need for a plastic filter cone because of the risk of breakage, these are well worth the extra expense.