Installation is quite easy, but before you glue anything, make a few calls while driving to someone who is willing to help you to choose the best placement for the microphone. And make sure this is what you want.
Audio streaming from my iPhone is like hearing a CD, but when I receive a call, it's like I'm using a different device.
It may be a limitation of the bluetooth standard for compatibility with bluetooth headsets, but I really don't believe that.
The sound is muffled and of much lower volume, when compared to the volume of the audio stream. So much, that even with the phone call on maximum volume, I have to increase the volume on the car stereo to get it to the level of the music I was hearing. This takes almost 2 stars from a maximum of 5.
Also, you have to press the button to connect it to the phone when you start the car. This should be automatic on power up.
This is really annoying, because most times, I have to connect it when the phone is ringing, and it takes a few seconds. There goes the second star.
The large button, sometimes needs to be pressed quite hard, if you don't press it right in the middle. There goes another one.
You can skip musics when using it with an iPhone 4, but don't double click too quickly, otherwise it will be seen as a single click, and stop playing. A bit temperamental.
I only kept it because I have use to the extra USB port, and really had no alternative due to the location of my line-in (far from radio).