One of our mainframe engineers bought one and asked me for some assistance in programming it. IIRC the 16K expansion pack used to get very hot.
I had an Apple][ bought in 1979. For comparison with the ZX under-£100 prices - that had cost about £1800 with black&white video, 48KB of ram, and an Apple format floppy disk drive.
To get down to the lower prices before the ZX you had to build your own - like the "Tangerine".
About that time there was an explosion in PC magazines, exhibitions, and specialist shops. At one of the exhibitions we drooled over an Apple compatible Winchester hard disk of 10MB - priced at £2K (about £6K in 2018?).