You can NOT use any other card that the VW on. No if's no buts. It is as simple as that.
As for the update it is simple.
Download your maps from the above website.
While they are downloading go get the memory card out of the car.
Now create 2 new folders on your desktop, on named newmap one named oldmap.
When the maps have downloaded, move the zip file they are in to newmap folder on the desktop.
Using the tool of your choice (Winrar I use, there are many others free) unzip it into that folder. It may take a few minutes.
Insert memory card into reader (slide the "Lock" switch to unlock it) and copy everything from the card to the new folder named oldmap. That is your backup, just in case something goes wrong. Once it has copied from the card delete the files on the card or better Format it.
Now you can copy the files you extracted from the zip file onto the card. Once done remove card slide the lock tab back and insert in car. Turn ignition on and after around 30 seconds the new maps will appear on screen. Job done so you can now delete the 2 folders oldmap and newmap as you don't need them.
I have just updated my maps using the above method and always use that method. It really is easy to DIY with absolutely no cost.
As you say, the instructions are very straight forward. Download and extract the zip file. Copy the old contents off the memory card. Copy the new contents on in place of them. Stick it back in the car.
During the stage of copying the old data from the card, you'll see the format in which the card is expecting the new data (it wants the whole of the maps folder, including the folder - don't just copy the
contents)
I'm inclined to disagree about the "you can't use a different card, no ifs or buts", though. There are clearly some restrictions in place, but as a pedant I feel obliged to say that there is probably
some workaround, even if it is very difficult, and that would mean that there are ifs and buts
