Thanks Genghis
It was actually broquets in cars that got me onto this!
They are marketed and used quite widely by owners of imported japanese performance cars that struggle a bit on our hopeless 97/98.5 RON fuel. Jap fuel is 100RON as standard.
My car has them fitted as standard by the importer (Prodrive).
I was just interested in their origins and, if they do do what the manufacturers say, why don't we hear more about them?