If the Insignia's cutting edge looks led you to expect something special from its navigation system, well, prepare to be disappointed. In fact, it's a mostly ordinary DVD-based rig with its own set of shortcomings and irritations.
The only significant deviation from the norm involves the use of flash memory, allowing mapping information to be uploaded from the DVD. The mapping disc can then be removed from the drive, freeing it up for music. Our best information suggests that the system has 2GB of flash memory, enough for three to four sets of country data at one time.
That aside, all the usual features are present. You can choose to view maps in 2D or pseudo 3D mode. The usual routing options based on road type are available, there's a POI database of highly dubious usefulness and basic traffic data is provided by the RDS TMC system.
And, yes, as with so many factory-fit systems, postcode input is limited to five digits. In fact, even that limited functionality is well hidden. There's no specific input field for postcodes. Instead you must use the "City" field. It's the sort of unnecessary foible that makes the system difficult to get to grips with initially.