has anyone else tried Lloyd Walkers latest tweak

Perditty, The only thing I would take issue with is your use of the term "debate". Inert crystals either can or cannot affect RFI. The debate could be about whether they make an improvement in one's audio system; that would be a reasonable subject for debate.

cause of the perceived improvement would be the topic of the debate

I have not tried the Black Crystal tweak, yet.
So, I have no right to form an opinion about it.
Judging from this thread, however, it appears to be 100% effective--based on the accounts from people who, actually, have tried it.
None of the naysayers seem to have tried it. So, their opinions are uninformed, and, in my view, worthless.
A theory is worthless unless experimentation can validate, or, invalidate it.
That is how science works: theory, then, experiment.
I would be interested in reading an account from someone who has tried the Black Crystal tweak and found it not to be effective.
Slogging through the mire of endless speculation this thread contains is tiresome.

I suppose it should be mentioned that Acoustic Revive's little QR-8 smokey quartz crystal is also recommended for the cartridge body, along with other resonance targets of opportunity. Of course, be wary of over dumping.

From Acoustic Revive's web site:

"Quartz Resonator QR-8 is not magic or occult. Reason why the sound improves by using QR-8 is that because, by placing QR-8 onto an agenda which causes resonance, the resonance frequency of agenda changes and it stops any resonation. Agenda such as plug, connector, parts, equipment switch, equipment housing, and door in the room, windows, wall, floor and ceiling resonates by its particular resonance frequency and by placing QR-8 will change the frequency and stops the resonance. But placing QR-8 to an agenda which does not resonate, adversely QR-8 may cause it to resonate or to over dump. So you have to be careful where you place the QR-8. You can check if QR-8 is causing the agenda to resonate or over dumping by listening to the sound."

Maybe in one of the parallel universes(quantum physics), we could actually see the effects of the crystal.