I definitely remember one magazine-cover-mounted flexidisc from the Spectrum era, but it was a real hassle to get it to work: the spectrum had a 3.5mm audio jac

I definitely remember one magazine-cover-mounted flexidisc from the Spectrum era, but it was a real hassle to get it to work: the spectrum had a 3.5mm audio jack labeled 'EAR' that was designed to be connected to a headphone socket on a cassette player, and most Spectrum owners had a relatively small portable cassette player to perform that role (a dumb one with no dolby noise reduction nonsense - but with a good mechanical three digit tape counter so you could mark tape positions); on the other hand, to play the flexidisc into the spectrum would require wiring up the headphone output of your stereo system amp up to the Spectrum (portable record players with headphone jacks not really being a common household appliance in 1984) - which also needed to be wired to a TV at the same time. This definitely involved a certain amount of wire stretching in our house, and in fact I suspect may even have required unplugging the TV output while the disc loaded, then unplugging the headphone lead and reconnecting the TV to see if it had worked. There's definitely good reasons why cassettes were the preferred audio delivery mechanism for 8 bit games, even with all the trouble that rewinding and azimuth alignments caused.