I run an assistive device business in Australia and experienced in many aspect of hearing loss. The issue with any electronic device is that the product is only as good as the weakest link.
In a hearing aid the weakest link is the microphone. It is so damn small. For any of the initiated compare a large dynamic microphone with a lectern microphone on a podium. You can shove a microphone directly into your mouth and still get a good sound while the podium microphone always gets up peoples noses when they do not know how to talk into them.
Physic dictates the size of the diaphragm will naturally resonate at higher frequencies based on smaller sizes. Filtering is the only way to deal with this but the hearing aid is such a small device that it is hard to place good filter whereas body aids are easier. This is why many people including my wife love the older larger hearing aids.
Enough said I am going back to Uni to study Electronic Engineering as I am only a lowly Technician and I have a idea that after listening to Dave may make it open source the main idea is to deal with the microphone in a way to avoid recognition and allow people to wear the device in confidence. It involves my wife and her excellent crafting capability as well. It maybe so simple that I may just use it to gain my experience in Science and engineering and give it away.
For a minor plug not my website but my suppliers website these products from Bellman are the best I have provided in a long time. There are so many other alternatives around but performance is not as good. Unfortunately market power dictate these to be quite costly. www.bellman.se/audio