This individual Astrophytum cv 'Onzuka' is doing really well so far. It overshadows its 3-inch pot with a full 3.5-inch diameter. I'll repot it soon. I've heard from an advanced grower that he cuts off the taproot at a certain age, forcing the stem to grow smaller, less rot-prone roots. Sounds radical but I seem to recall he claimed everyone in Japan does this.
It's hard not to like Astrophytum cv 'Onzuka'. It has strange, white-speckled skin, its body is oddly geometric, and its flower is understated but beautiful.

Speaking of Japan, that's where this justifiably popular cultivar of Astrophytum myriostigma is said to originate.