My friend has one of these, but they never caught on

https://www.youtube.com/watch?v=P2syqXx97LE

I had a seaboard. They didn't catch on because the surface isn't very consistent, it's hard to actually hit a note and not bend without setting the "dead zone" pretty large, and the surface itself is just not a great texture to play on.

The ExpressiveE Osmose is proving to be quite popular. I have one, as do 3 other musicians I know personally. It's a very similar idea, but a lot more mechanical.

There's other options too. The Ableton Push 3, Linstrument, Haken Continuum, and a few other MPE synths/controllers all do a better job than the Seaboard by miles. The Osmose is my reccomendation for most people currently, based on the half dozen or so MPE controllers I've had my own hands on and it's price, but I'd love to get my hands on a Continuum.