Although I am loathe to disagree with Jack Innes, I will proceed to do so, much to my peril: he is correct on the Pakistani horn glut, and their authenticity.
That said, however, perception is reality. Most people are smitten with these old horns on old cars, they belong and are every bit in place with the old car. These horns add a nostalgic flavor to any old car, especially in parades. Kids love to honk them, and they turn the eye whenever that sound is heard.
Leaving off a horn such as this is much akin to leaving off modern tires: the original tires were much softer (and more dangerous) than those available today. Better to be able to drive these cars, than have them sit in a museum and tout originality.