My Hitzer also has the bimetalic spring controlling air intake. I first set up without the baro. for the same logic you expressed, ie. stove gets hot, air intake is reduced therefore no runnaway fire, even when the wind blows hard creating a very strong draft. My stove does work just like that. However I overlooked that there is more to maintaining an EFFICIENT fire than that. The good folks here convinced me that too strong of a draft will still suck air up the chinmey faster than a properly regulated draft.
I set up the baro. and manometer as recommended, and guess what... My flue temperatures dropped about 50* to 100* . The heat lingers in the stove longer and heats the house more and the chimney less. The result of our bi-metalic draft controls and a baro. damper is amazingly even and efficient heat output.