Clive Sinclair was totally brilliant, but unfortunately his judgement was always a little off.
The C5 was just a disaster - two slow and dangerous to ever use on the road. The idea of a super lightweight electric vehicle that can move a single passenger with a tiny fraction of the energy of a car does make good intellectual sense, but the C5 and roads full of cars and trucks just did not mix.
Where I saw his brilliance was in designs like the ZX80. It had something like 2K of ROM and in that program space, Sinclair fitted a full basic interpreter, a full software driven video display generator (the ZX80 used the Z80 dynamic RAM refresh counters connected to some resistors to make the video D/A, so no video display IC's were used at all), cassette tape data I/O, and probably a few other things I have forgotten. I have never seen anyone who could fit so much functionality in so little code and hardware. His first miniature scientific calculator was programmed on a TI chip designed for a standard basic calculator. In the same memory space that others fitted + - * / and square root functionality, Sinclair implemented Logs and Trig as well.
Richard.