FWIW, I think I bought my first one in 1995. The basic design is unchanged, but over the years the "bottle" has changed. For a few years it was a metal canister, which now seems to be discontinued. I ordered one last year and a plastic bottle came. The metal canisters are a little bigger and heavier, but they work better in sub-freezing temps. I was able to connect an old cannister to a new horn. The plastic bottles yield about 20 seconds, or 20 toots between fillups, the metal cannisters 30 and 30.

The newest horn I bought makes accomodations for fatter handlebars.

The horns seem to last about 10 years. before the plastic begins to wear. YMMV