go and look the up the price, they are deeply expensive, even for basic "make it louder" type aids.
Worse still, because they interfere with your ear, you tend to loose the ability to "steer" your hearing. This means that you can't tune out other conversations/noises or stuff.
The one good side effect of facebook spending billions on its (probably) futile search for practical and popular AR is https://www.projectaria.com/glasses/
Which is a (cheap) platform to do experimentation for AR type actions.
However it has eye tracking, microphone array and front facing cameras, so it can be fairly easily modified into being a steerable microphone.