@Gero is correct. Improved accuracy compared to the quadrilateral kinematics using the original brackets to mount the chains to the sled.
There has been a comparison between the 45˚ kit and the top mount. MeticulousMaynard did an excellent job documenting his comparison. You can read it here: Triangular Linkage Evaluation Criteria and Measurements
Spoiler: “So my conclusions on the comparison between systems is that I think the 45 degree is a better system all around.”
Since then I think there have been some improvements made to the top mount design but I don’t think anyone has tested them again since then.
There have not been any head-to-head test with the linkage and the ring that I know of, however, several people who have had both the 45˚ linkage and the ring have said that they prefer the linkage because they tend to get wavy horizontal lines with the ring. Without testing, I believe this is due to “jittering” rollers, which is explained in this post: Throwing my hat in the sled modification ring