I’ve got a bin full of bad motor boards that I’ve been meaning to test with (the ports still work but they don’t spin the motors). From my experience, 5mm ferrite cores clipped within a few inches on the brain end of the cable are very effective at reducing ESD damage on boards. I have only ever had one port die when using them in the last three years and that was on the absolute worst field I have ever seen in terms of static (significantly worse than 2013 nationals). In that time I have fried at lest four motors and over a dozen ports from static when I wasn’t using ferrite cores.
I have done some very unscientific testing which involved shocking myself repeatedly. I found that when I gave myself a static charge and then grounded myself through a V5 cable that had a ferrite core clipped on the end, I never felt a shock, but I also no longer had a static charge (didn’t get sapped when touching ground afterwards directly). I also tested the cable with no ferrite core, which shocked me every time. I repeated the experiment several times with the same results. I am led to believe that the ferrite cores help dissipate most of the ESD into heat, since it is technically a high frequency signal which they are designed to block.
I personally think they fall under R18 point F:
Commercially available items used solely for bundling or wrapping of 2-wire, 3-wire, 4-wire, or V5
Smart Cables, and pneumatic tubing are allowed. These items must solely be used for the purposes
of cable protection, organization, or management. This includes but is not limited to electrical tape,
cable carrier, cable track, etc. It is up to inspectors to determine whether a component is serving a
function beyond protecting and managing cables.
I would argue they protect cables from ESD. They do not require any modification to the wires and can be removed quickly and easily if needed (although I have never had to remove them at a tournament).