Tuning Collars on speaker cables - concept and any good?

Back in the day, when Simon Rattle and I used to hang of an afternoon, we listened to his early recording and critiqued them on a Bose Wave that he loved.

Gosh, you’d think he’d be deaf. You know, what with all the high decibels.

Tuning infers a process that is somewhat predictable. Randomly mucking with the signal passing through a cable sounds like playtime for bored audiophiles.
Not that there’s anything wrong with that. Trying to distort your signal in a good way that is.  Fun! 😘 Fun! 😘Fun!  😘

Tuning collars are awesome for people who don't understand the difference between common mode and differential mode signal rejection.

Common mode noise is noise that appears on both signal wires equally. If the signal appears on both signal wires equally going to your speakers, then the "net" signal is 0 ... i.e. they will have no effect on the sound (at all).  Now, if your speakers were "grounded" which pretty much no one does, then there would be path for the common mode signal to go, but still ... same signal on both wires, so the speaker would not notice.

Why does this matter?  Because these "Tuning collars" go over both wires and hence can only impact common mode noise/signals.  Now, one could make the weak argument they reduce EMI, and that would be true if there was a ground path for high frequencies, but your speakers are not grounded, and your floors are probably not metal (and grounded), so there is not even a good capacitive path to ground for them to make any difference. I am sure there will be some made up argument about transmission line effects .... but I already sold all my swamp land in Florida.

Why is "real world" in quotes? Are you in an artificial world?