Fun effect: When finally confronted with the page-leave dialog, I automatically went for the non-default, grey option button – and was kind of surprised that this wasn't the option I wanted.
I've a minor criticism: The "No thanks" button should really be "Remind me later" and possibly greyed out, since any negative wording is allegedly bad UX and users must be protected from any blunt denials in any options. "Maybe later" is also acceptable and even empowering, since this places users on equal footing as they are now lying to the website just as this is lying to them.
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