There were problems with durability, reliability and overheating (despite appearances, the black stripes visible on the top rear of the case are merely cosmetic, and are not ventilation slots).

One advantage to using monochrome video is that different colour broadcast standards (e.g. PAL, SECAM) simply weren't an issue when the system was sold outside the UK.

When running a BASIC program, or when pressing a key during editing, the tv-display would therefore blank out (lose synchronisation) momentarily while the processor was busy.

These had to effectively replace the video rountines in ROM and embed the same in the normal program logic with exact timing, which is extremely cumbersome.

The same slot bus was continued on the ZX81, and later the ZX Spectrum, which encouraged a small cottage industry of expansion devices, including memory packs, printers and even floppy drives.

[15] One common modification by hobbyist users was to attach a full-size keyboard, optionally moving the motherboard into a larger case.

[4][10]) Kilobaud Microcomputing liked the design of the preassembled version, and said that the screen flickering during input or output was annoying but useful as an undocumented feature, indicating the computer functioning correctly.

It praised the real-time, interactive BASIC syntax checking, and reported that the computer performed better on benchmarks than some competitors, including the TRS-80 Model I.

The magazine criticised the screen blanking during program execution, small RAM size, inadequate built-in Sinclair BASIC, and keyboard, and recommended against buying the kit given difficulty of assembly and because purchasers did not save money.

Owing to the unsophisticated design and the tendency for the units to overheat, surviving machines in good condition are sought after and can fetch high prices by collectors.