I’m inclined to agree with Questscher. On the other hand, I see the problem that Lowboy is raising: we don’t want to say that all these instruments are melodicas, but it might be useful to have a general term that covers the “family” of instruments that are closely enough related to the melodica to be getting attention here. “Keyboard mouth organ”?
But I think “melodica” is the right word for melodions and pianicas, which are clearly the same instrument.