I've had hearing aids for about 6 years. The technology definitely works. It has to be activated in the hearing aids to use. There is a variation called a "neck loop" which allows an audio signal to be injected to hearing aids via anything that can be connected to a 3.5mm plug. I don't see this tech discussed often maybe because people are ashamed of wearing hearing aids. I feel no such shame.
I always wonder if these actually work
Yes, they do. Once we have managed to lost one and we got immediate feedback.
(What I want to say, is that people expect them to be functional, so I make an assumption that this expectation comes from past encounters with the loops being functional)