Interesting idea! Though since it doesn't have a more ergonomic keypad-like layout, but repeats the slanted mistake of default keyboards, and requires software companion, what's the advantage over adding math layers to your current keyboard, where you also have access to more keys and modifiers?
Seconded. This looks like a fun toy, but it solves a problem that I don't have (and I believe I am the target audience). Modern typesetters are very good (e.g., TexMacs). There is also a limited set of characters by design, and I would have to remove my hand from my keyboard only for those.