1. Size Issues
The first, most obvious drawback of an invisible hearing aid is directly tied to its chief advantage. Because they're significantly smaller than most other hearing assistance devices, they tend to lack features like on-device controls. People who struggle with manual dexterity may also find invisible hearing aids difficult to manage and handle, and some models will likely be too small to fit in some people's ears.
They also tend to have shorter battery life compared to larger models, and cheaper hearing aids may lack features like binaural coordination, Bluetooth connectivity, or rechargeable batteries.
2. Cost of Invisible Hearing Aids
Generally, if you want to purchase an invisible hearing aid with all the same basic functionality as a traditional device, you're going to be paying a hefty premium. Miniaturization is expensive, after all. Especially when you're working with complex, highly-sensitive, fine-tuned electronics of the sort you find in most hearing aids.
Unless you're willing to accept an incredibly limited feature set, this means you're going to be shelling out a pretty penny for your hearing aids.
3. Potentially unsuited for Severe Hearing Loss
Hearing aid technology has come an incredibly long way since its early days. But we're still not quite at the point where an invisible hearing aid is as powerful as a high-end, full-sized device. What that means is that if you're suffering from severe or profound hearing impairment, an invisible hearing aid will likely be insufficient.
Generally speaking, invisible hearing aids are best suited for mild to moderate hearing impairment, and start to fall off sharply in effectiveness after moving past that threshold.