That shape must be patented or copyright protected, because all the Amazon listings are several hundred dollars each. The usual knockoffs are conspicuous in their absence.
AFAIK the required precision for it to work is quite high.
Indeed. The Wikipedia article says: "The gömböc, as the first physical example, is less sensitive; yet it has a shape tolerance of 10−3, that is 0.1 mm for a 10 cm size."