That article is on the Green Sparkplug co website under "Technical" "New plugs".

I also think modern NGK plugs don't work well with magnetos. I then tried the same new plug on a bike with electronic ignition and it has bright blue spark, and no spark on the mag. Tried an old Lodge plug on the mag and it worked ok. I wondered if there was too much resistance.?

email (option): horror@blueyonder.co.uk

I use NGK in the M20 and often flood it to start. Never had a problem except sometimes it takes two kicks before it starts ;-)