In addition to reading “ad copy for a harmonica that reads rich melodica-like tone!!” I look for a day when the spell checker stops trying to correct me when I type the word “melodica”!
Of the suggested criteria to include in a review, I think air tightness, keyboard action, keyboard and tonal evenness, tuning stability, reed response, moisture resistance and ease of playing chords are the things I count on to hear about from players who had experience with the instrument. I agree it may be hard to describe tone color, but think that we should try at least for a few broad categories.
reed moisture tolerance
evenness of tone
number of keys (listed in description).