Dactyl/Dactyl Manuform is concave. Even more, its shape is programmatically generated, so you can separate control curvature for each axis, stagger, etc. It is

Dactyl/Dactyl Manuform is concave. Even more, its shape is programmatically generated, so you can separate control curvature for each axis, stagger, etc. It is literally infinitely customizable.