Can I use the A+ images outside Amazon?

They're built from your book, so you're free to use them elsewhere — but they're designed for Amazon's A+ layout (specific bands and proportions), so they may not be ideal dropped into other contexts.

For general marketing — your website, newsletter, ads, social — the mockups are usually the better choice, since they're made to stand alone on any background. Use A+ images for Amazon, mockups for everywhere else.