As Marje said - "I borrowed one and found I couldn't get on with it at all, whereas with a melodeon the basics all fell into place very quickly."
The opposite was true for me. A 'tina was easy, the melodeon was almost impossible without even trying to think about song words!
I found a toy melodeon for a few dollars in a junk shop a couple of years back. I does work properly, it's just very small and basic. Even so, the *#+!!! thing frustrates me and it's now consigned to the music cupboard. I might just give it to my grandaughter (aged 2) to play with. If you lived closer, I'd give it to you!
The best advice is try before you buy.
Robyn