Decades ago after an electronic music history lecture in Ottawa, I had the chance to play an Electronic Sackbut (by Hugh LeCaine) for a few minutes. Maybe it's because I play guitar but I had often found my hands rocking side to side for (imaginary) vibrato on piano keys. The (monophonic) Sackbut had keys that moved side-to-side bending pitch and up and down for volume and it was just the most natural keyboard instrument I'd laid hands on. Making vibrato at whatever speed and pitch bends was simply intuitive and a joy. Nothing afterwards has had that feel, but the Seaboard looks like it has a very similar approach. Space and cost will be large barriers for me to buy one, but I'd love to try one out some day.