This is my experimental ortholinear layout made with this kit. The UK layout is shown, it also works with the US key mapping.
The concept is aimed at inveterate two-fingered typists and it is guaranteed to drive those who hit the space bar with their thumbs to distraction! The red keys are symmetrical left to right and carry all the non-typing functions. Tapped, they produce space, return, tab and destructive backspace as shown on the face. Held down while another key is tapped they act as the four modifier keys. Chords of two or more red keys act as layer-shift, for example the characters on the front edge of the green keys are accessed by holding down the 'space' and 'return' red keys simultaneously (on either side).
So far I am finding this very ergonomic for my typing style, but there are issues, for example multiple modifiers (ctrl+alt+del) require complex work-arounds which are not easy either to type or to remember. I do have these keys duplicated on my mouse which strikes me as a better solution anyway (although such mice are sadly rare).
This does require some firmware modifications and I've not yet got my head around how to publish them on GitHub, but if there is any interest I'll put some more effort into that.