I purchased the single din parrot head unit RKI8400 which has radio and digitial media (no old school optical support) into a Skoda Fabia.
I use my android phone for directions (google nav), music (spotify), phone calls as well as reading text messages to me as I drive along. Now the Parrot provides 1 features which is not available in the factory fitted Sony in my S-Max and that is auto switching to the bluetooth device when audio plays.
So for example: I am listening to a particular radio station, MP3 on sd-card/usb stick or even an old iPod and the phone wants to give directions or read a text to me. When the phone starts sending audio the parrot unit switches over automatically to the bluetooth audio and afterwards switches back.
So I can have the music nice and loud and not miss a turning or message not just calls.
If other units listed here do this please let me know I think its an overlooked features which can turn your phone into a great car companion.