I wonder if overall quality of execution may be a part of the "big Mellotron vs. little Mellotron" debate. It's immediately obvious just by appearance that the big beasts are designed to be beautiful works of art, and I'd be willing to bet that the attention to exterior detail extended to the interior of the instruments as well. The M400 series is clearly a "working class" instrument designed for the rigors of the stage rather than to be set up in a wealthy person's music room. Add in the palette of sounds that is twelve times larger in the big ones, the built-in speakers and amplification, and clearly there is an instrument that is designed to be a statement in and of itself. All I can say is that the first time I actually touched a Mellotron (a new M400 in a music store in Albany, New York around 1973 or so) I recognized THAT SOUND as being inside that little box. Maybe it's not as warm or as versatile as the big one, but it's still THAT SOUND and NOTHING else makes it.