The general comments/guidance(attributed to Boeing Instructers)is 'If the engines working use it".
Both in the engine fire on liftoff case (to the safe altitude 400-800)before the 'drill',and in the 'reject' case until stopped.
And if the 'fire'occurs inside the FAF/OM,canx the bell,don't 'screw with it'until touchdown(reject scenario)or on the 'go-around'(takeoff scenario)
