They both require an expert to set them up; otherwise they won’t work properly. Here’s a quote from a cello enthusiast website: “The angle of the fingerboard, the planing of the fingerboard under the C string, the precise placement of the nut, the bridge, and the height of the strings over the fingerboard are all crucial dimensions, and must be set up by an expert or the cello will be virtually unplayable.” There’s more, but you get the idea.
So when you want to hear better you can go to a hearing aid specialist who will do what the computer tells him to do to set up your hearing aid. Little expertise is required for this and the hearing aid may be “virtually unplayable.” Or you can go to an audiologist with training and experience in hearing aid fitting, probe microphone measures, and the auditory rehabilitation process and get better results. Your choice.