Please make sure (for long term reliability) that (when installing NTG4/4.5 - not needed for 2.5) the extra fan subsystem is installed, otherwise units get too hot. Also if you want MB to be able to service/update unit then you'll need to ensure they update the Datacard (data record at Mercedes) and of course you want the unit updated to latest firmware and maps, and the instrument cluster coded to enable NAV menu and the time sync from the GPS.
Richard