You can download much, much more free e-books from Amazon.com (like hundres of pages in different genres), whether if your Kindle is registered in the UK, you get only 3 or 4 pages of free books in Amazon.com.
I did try both (I live in Europe too) and I found the US registration is much more useful for me. I "bought" so many books with a 5-star rating for $0, it's totally worth it.
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