640x400@70Hz monitor (not 100Hz as OP claimed) was the second part of the puzzle. You want as much readable non headache inducing (interlaced Amiga) text on the screen for music sequencing. Not to mention Atari ST _with_ that monitor was still substantially cheaper than naked Amiga 1000.
Whoa, I was very sure that the SM124 did 100Hz, but you're right. I stand corrected! And I agree that the combination of the great monochrome monitor and the built-in MIDI made the ST much better suited as a music production machine.
