I have a good friend who is oral deaf. He can speak almost like a hearing person, almost perfect. All his life he wore hearing aids. Two years ago he got a CI. He went to therapy, etc. to get used to it.
He tells me that it doesn't work for him. His brain simply cannot interpret sounds the way he wanted it to. The CI specialist just shrugged his shoulders and said, "It wasn't meant to be."
Another friend of mine is very easily his twin. They are alike in many ways, and she also wanted a CI. She got one and almost immediately loved it. She now is getting another one.
It puzzles me how some people benefits from it, and others don't. They keep telling me, some people are wired for it...some are not.
I think this is what some of the posters are talking about when they say they want a "guarantee" that this will work before they choose it for themselves or for their child.