Seasons Greetings DrMiles
I had the same questions as it appears to offer lots but it's very vague about exactly how it works so I set up a dedicated wi-fi in the car (old Alcatel Y800 and a PAYG data sim) - USB power plugged into the rear 12V and the Y800 held in place under the centre console by two blobs of blue tack. You cannot accuse me of over engineering the installation :lol:
POI transfers to the car seem to work OK if you select the right format but it is slow for large files, even on 4G - I ended up hooking up to the house WIFI which gave me a better speed and costs less in data. Up loading specific POI's and/or routes to the car seems to be reasonably quick at the PC interface but overly complex to access them in the car's menu driven interface.
I think the idea was that if you are "on the road" your office can upload a couple of new co-ordinates for you to travel to - not really focused on Joe Public
For bulk POI's (safety cameras) the alternative is to use a conversion system which VW have on their web site (in German) and this allows you to convert from a Merc file format and load via the SD Card.
It claims on-line traffic conditions but I'm just not certain that the main navigation system uses this data, I think you have to use a second mapping system which is downloaded as you travel and visually looks poor. Using the Android app seems to be slicker.
It also claims to offer more things like car parking and fuel and in this respect, it can find both - but you can get this data as a POI file or from Android, so I think it's limited.
I'm going to keep playing until the 15Gb data block is used but I don't expect to find anything that I cannot get on my phone

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Cheers
Earl