The general shape, two rings, flattened horn and machined-finish reeded mouthpiece are the significant features of the 'beater's' or 'harking' horn.
These (often machine finished) cylinders contain a vibrating metal reed which makes the noise when blown.
Reeds are also used in 'quack' ear trumpets usually in the form of small ear tubes.
Diaphragms are also used in some ear trumpets and notably the rare Aylsworth.
Also I recently found Chinese and Pakistan makers offering these as 'brass fog signal horn, brass hunting horn,
jagdhorn, corne de chasse, gamekeeper horns,
beaters horn' and ranging from £11 to £104.
I have also seen a reference to folk with large gardens using them to call kids to meals.
Older ones made in England were supplied by Acme