It is very nice to get a new feedback about the book function. The example already looks quite good. Here are some comments about Amphibious aircrafts.pdf from 08/17/2018:
1. the image size is too small for printing as a book (probably about 15x20cm book size). In the past, images took up the entire page width or half the page height and are therefore better suited for illustration.
2. the font size also seemed too small to me.
3. the link to Wikimedia Commons is too prominent.
4. the links are missing in the references. Without them, many references are useless. This applies in particular to the section "External links".
5. the articles are grouped in the preview. This results in "Article 5 of 4" in the footer on page 36.