A few notes here:
* This is intended to treat presbycusis, or old-age hearing loss, where the highest frequencies are lost first. It would not be effective for noise-induced hearing loss, where the frequencies around 4 KHz are lost first (the "s" and "f" sounds in speech). This matters in the low-income countries it's targeted for, because occupational health is not as strict and PPE is not as widely utilized, so people are more often exposed to damaging levels of noise at work.
* It does not handle loudness recruitment, a common effect of damage to the outer hairs in the cochlea which causes loudness perception to become non-linear. Someone with a moderate hearing loss would hear an 80 dB sound as just a few dB softer than someone with normal hearing, but a 40 dB sound as many dB softer than someone with normal hearing, and a 20 dB sound as not audible at all. So if you do what this hearing aid does and boost it all by 15 dB, the 20 dB sound becomes barely audible, the 40 dB sound is perceived as "about right", but the 80 dB sound is perceived as nearly 95 dB (really freaking loud). You have to have some non-linear compression in there to adjust for this, and not just overall -- it needs to be per frequency band (https://en.wikipedia.org/wiki/Bark_scale) to match the way the ear works.
* Another commenter mentioned that the "bandwidth to the brain" is not available. That's only true in the case of damage to the inner hairs of the cochlea. What's more common is damage to the outer hairs, which amplify the sounds, and that can be compensated for with a hearing aid.
What we really need is a common way to program a hearing aid, so we can have apples-to-apples competition. Right now, when you go to the audiologist, you get an audiogram, which tells you the minimum threshold of sound that you can perceive at each frequency band. But beyond that, there are proprietary adjustments for compression, noise reduction, profiles for different types of loss, and so forth. It's not like getting glasses, where your prescription fully defines the lens, and you can take it to any vendor and have them make it for you.
Edit: If you're really into this stuff from a technical perspective, http://refined-audiometrics.com/wordpress1/ is worth a read -- it's a project by an engineer who experienced a hearing loss later in life who has built a software system to make music sound right for him again, basically building a "super hearing aid" running on a desktop CPU to do more fine-grained processing than what is possible within the power budget and form factor of a regular hearing aid.
