The ring kit is provided for improved accuracy over the original “quadrilateral” kinematics setup (two L-shaped brackets bolted to the sled). The linkage kit you linked to was one of the first “triangular” kinematics (along with @dlang’s pantograph) that greatly improved accuracy and simplified Maslow’s world. @bar was working with the ring concept while the linkage kits were in process and he ultimated decided upon making it the new stock linkage. Which is better, @pillageThenBurn’s, @dlang’s or @bar’s has not been determined, but any of the three will be far superior to the original quadrilateral kinematic setup.