I owned Sinclair's programmable scientific calculator from a few years later which was similarly "interesting". It had 36 program steps (vs. 72 for the HP65 iirc), so storage system, and only one memory. Each constant in a program counted as N+1 steps where N was the number of button presses were needed. So it taught me about multiply re-entrant code.

I also owned a Sinclair ZX-80 (aka Timex) computer, later upgraded to a ZX-81 ROM with 16kB of memory.

Overall, Sinclair's problem seems to have been going a little too far in the "worse is better" direction with every product.