My ancient mill was Bosch and had a steel mill. Perhaps it was this particular product, perhaps in principle on the construction of a steel mill. In any case: The Kenwood-stone grinder grinds on the finest level significantly finer than my old mill. So I am very satisfied.
The price is (for a Kenwood attachment :) fine. The price difference from the steel mill (the indeed there Kenwood) is manageable. Because I would not experiment. Unless you want to grind oily seed. This is (I think) with stone not / not good.