First Book ai has helped me get my first book started, removing analysis paralysis and forming better structure and framework than I was able to do.
Likes: easy to use, quick to first outline, and decent draft copy, option for personalized stories adds warmth.
Caveats: lots of redundant sentences in the draft, typical ai verbage/formatting, and fairly verbose.
None of the caveats are bad, just be aware if you want it to sound less AI and more human you'll have several hours of proofing and styling.
Overall it's a win though, I have enjoyed the product and process.