I'd say the length is subjective, because that will change with preferred lever position for you.
What is very important no matter the shift rod length or type if rearset is that the linkage/shift arm interface maintain a 90 degree angle at rest- this provides the best leverage at the fulcrum.
In the pic, it appears to be a more obtuse angle, so you aren't maximizing the ability of the lever to transfer movement to the shift arm, which means inconsistent pressure for gear changes even if the qs itself is cutting/blipping.
Racetorx also makes a support that helps by adding a brace toward the outboard side of the shift shaft, eliminates a bunch of the flex which helps sharpen the response