Their wording is very confusing for me - "To opt-out from our anonymization of your personal information to perform data analyses, please provide your Mastercard or Maestro payment card number below."

To me it sounds like, "we are anonymizing your personal info, but you can opt-out and allow us to perform data analytics using your personal info as it is."

This claims the data is anonymized. I honestly don't really care if my purchases are analyzed in aggregate. I understood GP to be more concerned about personalized data being sold to advertisers. I certainly would be.