flash convertor?

i understand the "flash " aspects of the convertor. what i mean is why is the "flash" convertor supposed to be more efficent at highway speeds than a regular higher than stock convertor (say b&m holeshot , or any other brand) from what i have read the "flash" convertors are supposed to be better for both stall at launch and better for driving down the highway than the other brands of "non stock" convertors