Are killer cages easy to read on the page?

Yes. Cages are drawn as dashed lines inside the squares, with joined corners, and each total sits in the cage's top left square. The totals are checked to be 7 pt or more, as KDP requires; if they are smaller, the "Ready to publish" card says "The cage totals are X pt: KDP needs 7 pt or more. Put one killer on a page, or choose a bigger trim."