Let my just try to talk about the three-head thing, and one of you guys can correct me, because its old memory
In a 2-head machine, there is one erase head, and one shared-purpose play/record head.
In a 3-head machine, there is one erase head, one record head and one playback head.
Because of its shred purpose, there has to be some compromise in the single record/play head.
The great practical advantage of a three-head machine is that one can
monitor while recording: the music is recorded as the tape passes the record head, and then played back as it then passes the play head. The means that we know the quality of our recording in "real time." We can even flip the switch back and forth between source and monitor for comparison.
Getting my three-head machine made me very proud, but it was not only a symbol: that source/monitor thing was really, really useful. I made a lot of tapes in those days. Even the last car I had in London only had a cassette player.