I had the MDI kit added to my 2013 SE with the RCD 510 (Premium 8). I bought the kit online from a dealer for substantially less than my local dealer wanted to charge, and then had the local dealer install it. The cable is in my glove box. I probably could have done it myself, but didn't want to play with it on a brand new car.
I find the MDI cable to be much better than the streaming through Bluetooth because when I shut the car, the player stops. Not a big deal if you are listening to music, but I often listen to audiobooks when I drive and it is a pain if you shut the car and forget to stop the player and then need to figure out where you were.