I have a clover one bought on the late 90s, it is really sturdy and rotates smoothly. The layers are joined in such a way that it feels really solid.
I bought a larger size Creative Grids rotating mat but the top layer only just sits on the base and a 3mm high black disc - the layers separate so easily - really poor design & build - please avoid at all costs.
It is a shame because I love Creative Grids Rulers.