My Experience:
 FWIW; when testing the advance curves of Vlach and  RCexcl ignitions I had to remove a small section of the braided shielding of the HT cable in order for my clamp signal pickup to work.
At the same time I was testing, I was also charging batteries (Schulze charger).
When testing the Vlach, I heard an intermittent clicking noise during ignition test runs. It turned out to be my charcher switching on and off due to high power radio frequency radiation.
When testing the RCexcl ignition, no such thing happened, indicating less radiated HF didturbance from the high tension lead.

Both ignition types need a resistor. Vlach has it in the plug, RCexcl has the resistor in the plug cap.

conclusions?
I'm not that quick on the draw.