In some classes that require a "spec" esc...they will allow esc's like the tekins as long as they are in "spec" mode aka "blinky". The speed control blinks to let the tech guys no know its in spec mode. This spec mode allow no esc timing advance,so not to have an advantage over other escs that are legal in "spec" classes. Kind of a waste of an expensive speed control,but at least you dont have to buy another esc if you have a spare tekin like many of us do.