I've never used a flat matrix keyboard like the Ergodox or Typematrix, but I've been using a Kinesis Advantage2 for a few months which combines the rectilinear layout with cup-shaped "key wells" and a rather distinctive staggering of depth that keeps each key relatively closer to the fingers pressing them as compared with other designs. I'm not sure I'd want to use the key pattern with a flat board, because it's still not something I'm completely sold on, but I think it works well enough with the concave design. I really like the idea of symmetrical designs in general.