It is open to sellers enrolled in Amazon Brand Registry and is built from fixed module templates: banners, image and text blocks, comparison charts. Shoppers scroll it after the gallery, so it gives lifestyle images, close-ups and the brand's story room that the main listing doesn't allow.
The cost is the images. Each module has its own size, and many brands fill A+ only for their best sellers because shooting lifestyle and detail images per product takes too long. That leaves most of the catalogue with a bare description. Our page for Amazon sellers covers how we work with marketplace brands.