I've become very disillusioned with any form of car navigation system quite frankly and have experienced much of the trials and tribulations mentioned above whether it was installed in a Mercedes or the xf. I have been directed down very narrow country lanes through floods and even round in a circle as has also been stated by Bernard. One tends to rely far too much on the system and does not take in the scenery and landmarks so that when things go awry, one is completely flummoxed.
In the interim I have gone back to the old fashiond ways of planning my route via maps and with the help of my long suffering wife who actually seems to like playing navigator.
One other serious flaw with the Navi., is road works. Here it can only fail completely and I was totally screwed up in a city, called Bremen, which ended in me going round in circles several times.
I can only concur with Bernard again because I have also regularly experienced the navi. attempting to send me along country lanes and also via an indirect route, and also the wrong way down a one way street even though I have programmed the thing to take the shortest and fastest roads i.e. Autobahns.
I also found myself trying to work the navi. whilst driving along which is complete folly, I know, but I reckon everyone does it which is, to my mind, far more dangerous than telephoning.