I remember when I was a kid, I used to see those omnipresent infomercials for cheap "hearing aids." They'd advertise in the back of my dad's Scientific American and in my grandparents' magazines. And they always confused me: how could they charge $29.95 for a pair of hearing aids when I had to go to a doctor and be fitted with very expensive hearing aids?
For awhile I figured these were just hearing aids for old people. It took some time before I realized these were not "hearing aids" at all. They existed merely to amplify sound. Perfect for people who don't want to spend the money or go to the doctor - people who simply do not know any better.
This article confirms a lot of what is obvious about these sound amplifiers. Not only are they generally of low quality, they can actually further damage in the ear by amplifying sounds too loudly. They're not medical instruments, and no audiologist has touched them or adjusted them for the individual. They don't have to meet the same FDA standards as a hearing aid, and they don't have an individual fit.
Currently the FDA is defining regulations for these "Personal Sound Amplification Products." But I think in the majority of cases, a properly fitted hearing instrument is the best investment for people looking for treatment for their hearing loss.