Interesting layout, very cool experiment, not at all practical.
Actual typing speed
I’m lucky if I hit 10wpm.
OP mentioned they actually made this because they were looking for a good way to write during their long commute on the subway. They didn't mention why the on-screen keyboard was not an option. I mean, sure, it's not the most ergonomic IO device by any means, but at least it can achieve semi-decent WPM without extensive "training" and muscle memory development.
I feel like if you're going to this extreme, maybe a tiny stenographers keyboard is better?
I'd be more curious to see a mobile keyboard intended for the differently abled for who on-screen keyboards aren't an option