Compare the cost of this item and the original Sony Equipment microphone.
Big difference is it not!
I bought the Sony MEX-BT3700 because it had bluetooth built in and I wanted to use it to connect my HTC mobile phone so that I could be hands free in the car.
The Sony stereo has two settings for the inbuilt Mic, if it was set to high and the phone was in the cradle in the dash board it would cause feedback to the point where the person you were calling had difficulty in hearing you and echos prevented you from hearing them.
Keeping the setting of the inbuilt Mic to low I had to scream at the stereo to be heard.
I took a chance on this product because it was very cheap compared to the Sony manufactured Mic. It actually works really well now that I have mounted it on the door pillar of my car and routed the connecting wire under the dashboard. No wires visible. It is easy to connect, a wire on the back has a tag called 'Mic' just plug it in.
One word of warning though, if you switch the stereo setting for the Mic to high it will still feedback. Keep it set to low and it will work like a dream.