I think Melodica-Me is right that if you’re going to become a melodica enthusiast, almost any melodica will suck you in. The 37 key Schoenhut as not bad at all. I bought it to have some kind of keyboard to take to Mexico for a couple of months. Its conspicuous deficiency was that the sound thinned out toward the upper end of the keyboard. I was so taken with the instrument, though, that I knew I’d want to upgrade and so gave it away to the kid who did out lawn work in Mexico and ordered a Yamaha P-32D when I got home.
Many very good melodicas have been designed primarily for children. This is actually true of the P-32D, which is probably the most widely used melodica in Japanese elementary education, in which all children are required to learn to play the melodica. Almost all, if not all, of the innovative Japanese 25-27 key melodicas were designed to be marketed to young children. My guess is that this is also true of the small Italian melodicas.
I remind myself periodically that improving my playing is a much higher priority than finding a better melodica. Anybody with the money can collect melodicas — I do and I do, but it’s hard to become a decent player and humbling to hear what a really good player can get out of even the cheapest melodica.
Finally, experimentation is fun, but for serious differences in sound and playability, I think vintage melodicas are the place to go.