There are also 20,5mm stones. Not all gobans are compatible with the 21,5mm stones. But it shouldn’t be a problem if you buy them as a set.
Glass stones are shiny, yunzi are dim.
I own 7x20.5mm glass stones witch have a rather inhomogeneous height. I like the general height of them, but it’s mostly because I’m used to them.
I’m thinking about buying the half convex yunzi stones as a replacement.
Yunzi stones can contain lead Recommend Stones
They have a reference picture about the different stone heights. It should give you a decent impression of how the stones will look.
