Remember, the average joe thinks that all a hearing aid does is amplify what it hears over a broad range of the audible frequency range. While this may have been true when they first came out... hearing aids now usually just amplify the frequencies that the individual needs help in hearing. As we age, certain frequencied of hearing are lost. Very seldom does a person lose all their hearing accross a wide range of frequencies, unless there hearing has been damaged somehow. As well, hearing aids may even mix other frequencies into the input to cancel out other unwanted noise. I remember that my dads hearing aid helped him in noisy situations, pick out specific discussions...without his aid, it all just sounded like one big wall of noise. Its very simplistic to call this amplifier a "hearing aid"....just as calling the slabs of glass on the bottom of a Coke bottle " Corrective Lenses"\
My son actually has one of these amplifiers that use the circuit the OP has provided..except its called a "Super Snooper"
Its built into a wee tiny plastic bean shaped case around 1inch, along with a pair of headphones. Its supposed to amplify conversations so that you can snoop in on them, but its soooo noisy, loud and distorted...you cant tell what anyone is saying. They are available at Dollar Stores here in Canada, and come with a extra set of 2 3AG batteries to power the unit.