If you have command, you don't want it. UMI is for non-command or non-multimedia cars.
It gives you navigation and ipod interface and bluetooth streaming.
the universal media interface includes navigation, but I thought this was about the media interface (UCI) that is just about connecting ipod/usb/3.5mm audio jack through the most loop to enable you to have decent ipod playlists etc controlable and visible in the comand head unit (NTG 2.5).
For anyone interested in this, I read on a mercedes website that the media interface now supported ipod video display on screen, so long as you don't have a tv tuner connected.