If I had to shut down the turbine due to a fire, I would do it using the transmitter shutoff (closes both the fuel solonoids and kills power to the ECU) rather than reaching into a plane that is on fire
So would I!!. The 2 reasons for the manual valve, as far as I can see, is that you prevent the engine being flooded when refuelling and so that you have the means to shut off the engine following some form of ECU failure that leaves the pump running. It is a last resort shutoff only if the TX shutoff doesn't work.