There is a caution that comes with the valve, that the gas tanks must not have any debris or rust. Any debris or rust can clog the line faster than a stock line.
The fuel inlet of the fuel pump is above the fuel level, so gas cannot siphon back to the tank. Most problems with being hard to prime are due to vacuum leaks in the supply side of the fuel pump. These can be lines that the ferrule has not been soldered. flex lines that have small leaks or the gasket for the sediment bowl. These leaks will not leak gas, just air. The input valve in the fuel pump can also leak, and the pump will not hold enough vacuum to pull the fuel into the bowl when cranking with the starter. All of these will not affect the fuel delivery when the engine is running as the strokes are close enough together to overcome these small leaks.
I doubt that the check valve will help, except in the case where the fuel pump sediment bowl gasket or input valve is the problem. In these cases, it will work until the leaks get bad enough to fail when the engine is running. A new flex line will also fix many of these problems.