that’s an interesting question – melodica, pianica, melodion, accordina, Vibrandoneon, Eolina, melodyhorn, there are so many names for the same kind of instruments!
To me key-flute would be completely wrong (the Suzuki “A-25F Andes” is a key-flute because it is not a free-reed instrument but a 25-in-one flute played with keys).
A blow organ would be played mainly with two hands, as well as a blow accordion (a term which I read on http://www.akkordeon-maurer.de) – it would be a “blow-the-right-side-of-an-accordion-instrument”, but that sounds a little awkward, doesn’t it?
So, let me ask a simple question in return: where are we?
We’re at (or better: IN!) MELODICAWORLD! So shouldn’t we pay tribute to this site and its founder? In my opinion it should be MELODICA, nothing else…
Besides this, Hohner invented this instrument and gave it that name, the other names refer to “melodica” (piaNICA, MELOdion…) and the instruments themselves are based on the same principals of sound and construction.