Oh how we laughed when he tried to prevent the story getting back to the UK.
Light up might be immediate but the production of significant extra thrust isn't, a few seconds of extra stress in the event of one of RR's finest !!!!!ting the bed.
Certainly when tanking, and more oomph is required, light one burner then wait a few bananas for the thrust to come before retarding the donk left in dry. Pull the other back too soon and you fall out, too late and the tanker appears very large in front of you.