A friend of mine has one. I would be happy to ask her any questions you'd like to ask me.
For now I will just say that it doesn't seem to help much. She is still very hard of hearing and if she is not facing you she doesn't know you are talking to her even when you raise your voice. But I know nothing about how it works, or how she has it adjusted, or her medical history.
But as I said, I would be happy to pass on any questions to her and get back to you if you would like.