I don't have the hearing aids myself, but I've seen them in person and just love them. Very cute, they don't interfere with earrings, and they look just like the real thing. Of course they only come in pink and white, but most little girls with hearing aids choose pink anyway and I wouldn't be surprised if AG eventually puts them out in another color or two.
The main downside to the hearing aids is that they do interfere with glasses slightly--the doll can still wear glasses even if she has aids in both ears, but the ridges of a doll's ears are only so wide, and on a doll wearing both, one type of aid or the other is left looking a little precarious. This would probably be less of an issue if the hearing aids' ear hook (the white part of the current model) were thinner, especially if it were some kind of very thin, flexible tube that couldn't break. However, this would probably require more steps in making them, increasing the price yet more, and might make for a hearing aid that could fall apart.
The only other problem with these is the hole required to hold the hearing aids on (see above picture). It looks a little odd when the aids aren't in place (and will probably lead to some very confused collectors in the future!) but most dolls' hair can easily be styled to cover it. For customizers, it would also interfere with being able to fill the head with boiling water for eye swaps, but with some ingenuity the holes can easily be plugged temporarily.
Despite the problems, I give the hearing aids a solid A+; all the issues I mentioned are minor and virtually unavoidable, and it's awesome of AG to put out another piece of assistive technology for children who need to know they're not the only ones.