Henke,
A manual fuel shut off is a requirement in the AMA Turbine Regulations here in the USA. I know that adding fittings downstream of the pump is not advised. However, have you ever experienced a runaway fuel pump when the pump pours fuel into the model and tailpipe? A downstream shut off does nothing to stop the flow. However, a manual shutoff on the suction side will starve the fuel pump and help contain the fire. I have personally experienced a fuel pump runaway and it will be long remembered. Lucky for the quick shutoff and halon extinguisher, the resulting model damage was minimal-only a "technicolor" tail pipe.
Rgds,
Art ARRO