With Commodore-64 you also had to buy their tape recorder (same thing as with Atari 800XL), while Spectrum worked with any existing recorder, which every house already had at the time.
The advantage of the C64 tape recorder was it reliability and the motor being pilot by the computer. With personal tape recorders there was a lot of problems due to heads miss aligned.
As I remember from that time, all C64 users also had tiny screwdriver for adjusting head azimuth. Could be related to pirated tapes in ex Yugoslavia, copied on who knows what kind of equipment.
