Following the detailed instructions for updating OS on MKIII or MKIV I have never had an issue. I would be cautious about upgrading someone else's MKIII or MKIV unless that person was totally aware that there would be a slight chance of bricking the NAV unit. From personal experience its one thing to update the OS of an $50 wireless access point versus a $700 NAV unit.

What would you do if the person helping you bricked your NAV unit?

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E83 - Aero PKG Mods installed: Homelink mirror. CIS-IBUS video module, AUX, Rr Dr Release, stock wheels, Remote start, CarPC (Atom) & mud flaps - NAV - MKIV - NA Map DVD - 2011
E46 - 18.5 wheels/tires (summer), 17 stock (winter), Homelink, NAV software upgrade, BMW video module, Radio to V53, AUX, USB IBUS interface,BMW alarm install, CarPC(Epia), remote starter, tank battery & angel eyes. NAV - MKIII - NA Map CD - High Version 2008.1