I'm pretty sure the Focus horn is the Low tone version. It has an L that is in a circle on it as seen in my picture. I saw an H on the Harbor Freight Fiamm horn in the same spot.
About the air horns being disposable, maybe they are. But at 17.99 and 12.99 on sale, I won't mind to much since the hard part is the initial install. My other car has had them for around two years now and they still sound excruciatingly loud.
I'm a middle aged guy, with a middle school mind.