This app is actually excellent at what it does and doesnt promise anything that it doesnt.
There are complaints that its too expensive. I would tend to agree, but no-one is forcing you to buy the app. Its your choice.
The app itself is rather clever. If you have BT phone calls, but no audio streaming, it connects to your Bluetooth as a phone call, but without actually dialling a number.
The audio quality that you will receive is exactly the same as your BT phone quality. In addition, the app provides sample music to test, which gives you a good idea of the audio quality.
Personally, I would not listen to music over this, but I find it invaluable in playing GPS instructions through my six car speakers. Much easier to follow, than if the sound is only coming from my iPhone.
I repeat: it wont boost your Bluetooth capabilities (if you only have 8 kHz, thats what you will get), but it doesnt pretend to. It does everything that its claims to, and I can only understand the many negative reviews as the result of misconceptions.
It does exactly what I expected it to (and what it claims to do), and does it very well. The one caveat is that, on a long trip, the combination of this app and your GPS app will use your battery pretty quickly unless you charge your phone whilst driving. However, that is to be expected.
Alex in Arizona about Blue2Car