Right now, when a books is finished being generated/rendered, it gives you a bunch of text with a bunch of links in it. One of those text links is the 'Download the file' link, but it is virtually lost in the text.
Instead it should show you a giant green "Download Now!" button, similar to the example here:
You could easily use our jQuery.ui library to make such a button. See the example at Wikidata here: