Customisable firmware. e.g. simulating different "layers" of keys to reduce finger movement, dual-function keys depending on whether the key is tapped or held (which allows for using modifier keys on the home row, reducing finger movement), etc. This can be done with software like kmonad; but I imagine that's less convenient than having it on the keyboard itself.

With the keyboard being physically split, your hands don't have to be so close together.

Also the row-staggering of more common off-the-shelf keyboards just feels so weird after seeing keys arranged in a grid, or vertically staggered.