First off, many thanks for trying it out and responding. Let me address a couple of the comments
There could be a couple of explanations for this. First one that comes to mind is if the hardware volume on the device is too low. We recommend people don't try the aid with maximum volume to begin with, in case the output is uncomfortably loud. However, once the device is running the volume buttons on the side can be adjusted to boost or reduce the level as necessary. The second thing that might make the experience sub optimum is using headphones with a microphone built into the chord (like the ones supplied as standard). These microphones are designed to pick up the sounds made by the phone user, not to pick up sounds in the user's environment.
You might have luck experimenting with different headphones. If headphones are used without a built in microphone, the app will default to using the mic in the iOS device. This might give a better experience. Also, different headphones have different sensitivity, meaning some headphones will sound louder at a given volume setting than others.
Noted. Thanks. This will need some serious thought. The app is already quite wordy with all the various information boxes, as I'm sure you've noticed. Perhaps some built in testing would get the listener to a good starting point from which they could try different settings?
I would not recommend daisy-chaining the BioAid output into another hearing aid processor. This is unlikely to result in a satisfying experience as the processors are not designed to work together harmoniously. However, many thanks for trying it out and reporting your experience.
This is all really useful and I'm very grateful for the responses!