The big question is: Do the bottles do any good if the actual fire is on the tarmac below the engine where the fuel pools...
For me the bottles are totally useless on the ground, and you should concentrate on other things (stearing the aircraft out of the wind so that fire/smoke spreads away from the fuselage, prepare evacuation, instruct cabin crew, instruct rescue services).
If the engine nacelle is breached, the bottles do almost nothing. Just polute the environment...