Tom Bliss is in a very small minority if he finds a melodica immediately intuitive. The fingering of the black-keys-on-the-left, white-on-the-right type is like nothing else and the piano keyboard type is no easier than a piano. The single reed sound is pretty harsh. They can work well as a chordal instrument, for reggae or (the way David McGuinness uses it) for Scottish music, but that means learning how to finger chords, and I can't think of any player who makes them sound good for tunes.

Many people can't get single notes out of a mouth organ. I can't, my lips just don't work that way. For us, it's an anatomical non-starter as a tune instrument.