Hearing aids have evolved so much overtime - it's hard to believe that a hollowed-out horn was the only option at one point! "Technology" didn't find itself in the hearing aid industry until the late 1800's with the invention of the telephone as the inspiration. It wasn't until the late 1900's technology was able to fit into something that only fit on your ear vs a device with wires you had to clip on your pants.
Technology is advancing so quickly since the end of the 20th century that the hearing aids of today are virtually invisible and have very little limitations on levels of customization available.