Your responses seem to confirm my concerns. To me it seems like another point of failure for something you only do once or twice a year. Also, the whole thing seems to scream cheapo mod that will fail. You have to wonder why no manufacturers have any kind of factory valve installed. Yea, the gasket and bolt is easy enough and cheap, but you would think 1 manufacturer would try it if they could make a reliable valve.
I also worry about how temperature changes from the ambient temperature to standard operating temperature of the engine might affect the valve and its seals.