See github.com/arrowtype/NLI-test for details and a written explanation.
Allows curved interpolations while being reasonably simple to design. Has some limitations in rotation.
A bit harder to make, but able to do curvier interpolations up to 180-degree rotation (beyond this, you would need an additional dimension or an additional step).
Much simpler to make with existing tools and useful for many things, but totally unable to do rotation.