What Kindle Create does well
Kindle Create is free, comes from Amazon, and turns a Word manuscript into a Kindle book without any typesetting knowledge. It detects chapters, builds a simple table of contents, previews the book on phones, tablets and Kindle devices, and offers four themes. When you upload a print book, KDP calculates the margins and adds page numbers for you.
For a text-only novel that will only ever be sold on Kindle, that is a lot for nothing. If that describes your book, it is a reasonable place to start.
Where it stops
The limits appear when you want control or reach. Kindle Create's four themes cannot be edited. For a paperback, Amazon says you cannot change the margins, the font, the font size or the line spacing, and paperbacks with tables, footnotes or endnotes are not supported. Preparing the ebook and paperback from the same manuscript is still a pre-release feature.
Kindle Create can export an EPUB for reflowable books, but its preferred format is KPF and Amazon lists publishing outside Kindle as unsupported. It also does not make covers, so the cover, the spine and the back-cover copy are handled somewhere else.
Where Coverfairy fits
Coverfairy runs in the browser, so there is nothing to install. Import a Word file or EPUB, choose a trim and one of eleven genre themes, and page through the typeset book with a live page count. The same project designs the editable cover and calculates the spine from that page count, so the paperback cover is the right width for the interior you just formatted.
Formatting is free to try with a watermarked sample. A $6 Week Pass or $12 monthly plan unlocks the clean EPUB and KDP-ready print PDF along with every cover export, so the ebook can go to any store from the same project.
Which one to choose
Choose Kindle Create if your book is a simple novel, it will stay exclusive to Kindle, and free matters more than control. Choose Coverfairy if you want to adjust the paperback, sell the ebook in other stores, keep the cover and interior in step, or work on a Chromebook or someone else's computer.
You can also use both: draft and check the Kindle reading experience in Kindle Create's previewer, then build the finished print edition and cover in Coverfairy.
