I format eBooks as a service in my business and always wondered whether my method was the same as others. I downloaded this book to see how other people suggest formatting an eBook and was surprised at the complexities of the process used.
I follow the Smashwords Style Guide and so far have not had one book refused for premium catalogue entry on the first attempt. I have picked up a few tips along the way to add to the style guide but I don't think it's necessary to use both Calibre and Sigil for a perfectly formatted eBook.
I will however test this process and see how it compares. However, the book is a very clear guide and I am positive it will help a lot of authors/writers to produce their books for the variety of formats needed.