GasStop will completely (100%) and automatically shut off the supply of propane in the event of a major leak or catastrophic regulator failure. The excess flow valve is essentially a spring-loaded cylinder that acts only if the flow is over 200,000 BTUs/hr. If the flow is over this amount, the valve is triggered and stops 75-90% of the propane flow. So, what about the remaining 10-25% that is not stopped? This propane still flows and can quickly fill the RV up if there is a major leak, so it does not offer the level of protection needed in RVs.