33coupe: Thanks for that.
I issue I have is that I can't see why I should spend $400-800 on a head unit that doesn't do any more than copy my screen.
I'm not sure if you mean "screen mirroring" (the head unit just mirrors what showing on your phone) or if you mean the head unit has the same functionality / apps as your phone.
On my stock steering wheel, I have radio volume, source and phone answer. I used a Connect2 adapter so I could use the existing wiring and buttons.
Plus there are dedicated buttons on the head unit.
Lastly the unit support a rear view camera, when you put the car in reverse. It also gets speed from the speedometers, which helps the GPS do slightly better.
I also have an external microphone permanently attached to a pillar, so my Bluetooth phone connection is better.
Though it's illegal to use while moving, most Chinese head unit support playing video DVD's also.
So it does have a few advantages over just a phone.