Maybe it’s silly to criticize the security, but they could have chosen a better 12 permutations for the system. For instance, keys 3-4 and 6-7 only differ at 6 positions. Better to choose starting positions so that fewer pairs are shared between keys (e.g. starting at 1/I/4/N/7/S/0/X seems better, although I haven’t done a thorough analysis).

Are you sure that flipping on the short edge is correct in your PDF? In the book it looks like the back of the sheet is supposed to be upside-down (so that it can be folded to show 1-6)