I have compared the "US" version available at GCW to the "English (UK)" version available from Atari (yes, I have a valid pre-order key) and they're IDENTICAL.
Code:
C:\temp\nwn2-preorder>md5sum *
171b580682ead0f68d972c499f3450a4 *NWN2-PRESALE-BONUS-UKGB.EXE
171b580682ead0f68d972c499f3450a4 *NWN2-PRESALE-BONUS-US.EXE
I had already successfully installed the GCW file in my game. Haven't found the merchant, but if you do install and check your character traits screen you should find a section called "Merchant's Friend" which says that you get 10% off of merchants and access to a special merchant somewhere.
It's kind of silly really, because all it does -- as far as I can tell from a cursory look -- is install two very small (~1KiB) files. It's safe to say that many of the resources required (graphics) was already shipped with the game, this is just an "enabler".