has anyone else tried Lloyd Walkers latest tweak

The fact that the (3, one assumes) black diamonds are used on the underside of Walker's record clamp suggests that vibration control is the mechanism, at least for the record clamp, perhaps for the cartridge, too. The fact that folks use crystals in areas where EMI/RFI is present doesn't necessary mean crystals work by absorbing EMI/RFI since, as it turns out, many of those locations also contain significant levels of vibration,me.g., power cord plugs, circuit breaker boxes, in proximity to small electron tubes, on top of speaker cabinets, on transformers, etc.

Lewm -
The answer to your scepticism lies in EMI not RFI.
Anything that emits/uses RF will emit electromagnetic noise. Even things not designed to use RF if resonating can emit electromagnetic noise.
The piezoelectric properties of a quartz crystal make it usable as a resonator. Therefore the process is twofold in terms impacting the environment around the cartridge.
1. It absorbs vibrations and will emit EMI when excited or resonating.
2. The EMI emission from the crystal can alter the behaviour of other EMI floating around in the vicinity.
Now you could question whether this phenomena can be heard in an audio system, but the alteration of EM noise around the cartridge using crystals is basic science.

Rauliruegas
all of what you suggest has been done with wife, children, and quests all who have no interest in high end audio and all have had to pick their respective jaws off the floor!
AGAIN the reason for the post in the first place was to see if anyone else [with whom I have no connection] has had a similar experience.
two and counting

Yes, quartz crystals (of any color) do have piezo properties, as do a few other crystals to differing degrees. They have been used successfully in some power cords and some small black boxes when placed strategically in a system.

So I'm not surprised that they may work when located near a phono cartridge, which is a very sensitive instrument. But I don;t know what Lloyd's black diamond cut crystal has over a regular quartz crystal, other than it probably looks nicer.

So I tried attaching a reasonably sized clear quartz crystal to the front of my cartridge (a Transfiguration Temper). Of course, the arm had to be rebalanced and tracking force adjusted and such to compensate for the extra mass at the headshell.

The end result - I can't hear anything different, but then there is no way to easily A-B this tweak. It does look very odd, like a pimple on my cartridge face. I think the next step is to remove it, and readjust and see if I hear anything going the other way. Maybe some time this winter when I have time.

Dover wrote,

"The answer to your scepticism lies in EMI not RFI.
Anything that emits/uses RF will emit electromagnetic noise. Even things not designed to use RF if resonating can emit electromagnetic noise.
The piezoelectric properties of a quartz crystal make it usable as a resonator. Therefore the process is twofold in terms impacting the environment around the cartridge.
1. It absorbs vibrations and will emit EMI when excited or resonating.
2. The EMI emission from the crystal can alter the behaviour of other EMI floating around in the vicinity."

Problem is piezoelectricity, by it's very definition, is the conversion of mechanical pressure to electrical charge, not EMI. Besides wouldn't one wish to reduce EMI rather than increase it? Hel-looo!