As far as I remember it should be the other way around: Sinclair had analog audio input/output so one could hook up a turntable instead of the tape. Commodore 64, on the other hand, had a proprietary tape recorder called Datasette so there was no way to hook up a turntable to it. Of course, one could always just copy the signal from a vinyl record to a casette tape and then play it back to the computer.

These records that were stuck to magazines were annoying as hell. They are made from the thinest sliver of plastic, the thickness of a candy wrapper, and would invariably have suffered some sort of kink in them on their way to the store. I can't remember if I ever got one to work properly with my Speccy.