has anyone else tried Lloyd Walkers latest tweak

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.

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!
Geoffkait (Threads | Answers | This Thread)

Hel-looo
Where there is electrical charge generated there will be electromagnetic radiation. I should have used "EMR" instead of "EMI" perhaps.

Here is some light reading for you.
I'm a little crystal short and stout

Lewm

when we just mount a crystal out in space on a cartridge or tonearm there is no electrical energy source to set the crystal into resonating,

In my view there are 2 possible sources of excitation for the crystal -
1. Any resonance generated by the cartridge when playing a record
2. Electromagnetic radiation from the cartridge generator.
Whether these are significant enough to excite the crystal - someone else can do the maths.

the EMI emission from the crystal can alter the behaviour of other EMI floating around in the vicinity

This is the basis for the "looney" brigade selling crystals for PC's to make you feel better. Whether it is a process of absorption of EMR or emission to change the fundamental frequencies of electromagnetic radiation is open to debate.
Remember a doctor was struck off by the medical association for suggesting smoking was injurious to health in the late 1800's and Florence Nightingale took 30 years to convince the medical fraternity that clean bandages and fresh air was helpful in wound treatment.
I try to keep an open mind in these matters.