I bought the XCARLINK module and I can say that the audio, from my iPhone to my RCD300 is great!!! (CD quality)
It charges, I can use the buttons on my mfsw and rcd300 to control it (volume, tracks, play, stop, etc.).
It 'emulates' a CD changer, so when I choose 'cd1' on the RCD300, it goes in iPhone mode and I can choose a track directly from my iPhone.
When I choose 'cd2' till 'cd6' the iPhone goes in accessory mode and I can use cd2 to cd5 as playlists, made on my iPhone.
I also have the BT addon, so it works as a good Bluetooth carkit. It is also possible to stream music from the iPhone to the xcarlink/rcd300. The quality is good, but you notice that quality is better when connected with the cable/dock-connector.
No parrot or other streaming bt carkit can provide this audio quality.
It just emulates the o.e.m. cd changer and it uses the internal rcd300 (or rn510) amplifiers.
I can also still use my o.e.m. cd changer, because you can switch between xcarlink and cd-changer.
http://www.xcarlink.co.uk/product.php?productid=4&cat=2&page=1(My iPhone 3GS sits in a leather Kuda Golf MKV console on the dash, so something like this:
http://fotos.marktplaats.com/kopen/c/23/s3UL3qLk1LeL3rVIA93bQg==.jpg)