So, I now know what the "volume control" on the Airzound is actually doing physically, and I know that it might be smart to leave it on full volume regardless, and I know that some Airzound horns have manufacturing defects, and I know that there are other options for noisemaking and general safety devices.

But I'm still interested in my original question. Does the volume control (or pinch valve or whatever you want to call it) on the Airzound actually function effectively as a volume control? Does it modulate the volume of the horn significantly?