If factory navigation isn't a priority...as the others already mentioned...the MID (multi-informational display) controls all the AUDIO/DSP/CLOCK/TIMER/OBC/PHONE functions just like the navigation screen.
The biggest difference is...the Nav screen has a built-in cassette tape player behind it...with the possibility of an optional 6 disc CD changer in the back. If you get a face lift e53 with the MID (in North America)...it will have an in-dash single CD player with the possibility of an optional 6 disc CD changer in the back.
If you have a smart phone with a data plan...you already have a navigation system with you that is probably much easier to use and is probably more up-to date as far as streets & POI (points of interest).
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