This is really interesting, thank you for sharing! I wonder if it would have been more successful if it had just two rows instead. The duplicate rows add more power, but at the cost of adding ambiguity when sightreading, as you have to impromptu figure out what fingering you want to use. And it also makes it more expensive and intimidating looking. I feel like two rows would provide the core benefits while being more accessible. But I could be totally off, as I've never touched this thing.