I bought one of SkipjackK8's Black Diamond melodeons at Whitby this year, and I'm having great fun learning to play it.
I'm already a virtuoso at Twinkle Twinkle Little Star, and now I'm learning Bobby Shaftoe :)

I can pick out a lot of tunes on the right hand, but the difficult bit is learning to play with both hands. The base side is't easy to co-ordinate with the right, to start off with, but I'm getting there.
I joined a melodeon web, and there's a guy does a whole series of YouTube lessons, and they're great.
Daddylongles is his handle, and I wish to publicly thank him. The lessons are clear and concise.