I've got the Logitech adapter and also a cheaper 'Sandstrom' one from the purple shirt place (£17.99). The only real difference is that the Logitech has a pairing button (which can be annoying if you are always swapping devices as I do) and phono connectors as well as 3.5mm jack. I use one of the Sandstrom ones in my car plugged into the aux in.
There is a useful app called A2DP manager or something which allows you to connect to your audio device based on various things. For example when I get in the car and my phone automatically connects to the normal bluetooth receiver the app then connects to the A2DP one as well.