> His computers weren't aimed at middle aged adult engineers.
Maybe not Clive Sinclair's products specifically, but you'd be surprised with what professional engineers could use these 'toys' for. Keep in mind that machines with comparable featuresets could sell for huge prices well into the early and even the mid-1960s, and were used for real, sometimes critically important work.
Turing's Pilot ACE, that Turing considered didn't have enough memory for real work, had 32 mercury delay lines with 1024 bits each: that's four times as much memory as the ZX81.
Maybe not Clive Sinclair's products specifically, but you'd be surprised with what professional engineers could use these 'toys' for. Keep in mind that machines with comparable featuresets could sell for huge prices well into the early and even the mid-1960s, and were used for real, sometimes critically important work.