Let's just start by saying THE BEST way to view your books is using Book Creator's Read to Me mode, and by publishing your books online with our app. 😊
For that reason, we're not actively exploring ways to make Book Creator work with 3rd party e-readers.
We've already optimised Book Creator's fixed layout ePub files for reading on the Apple Books app, which is ideal for offline reading (but requires an Apple device).
Beyond that, there are limited known options for reading your Book Creator books on other devices. We know for sure that Book Creator books will not work on an Amazon Kindle, as they use flowable text format, not fixed layout. There are options such as Google Books, which we explored when we used to have an Android version of Book Creator. It seemed to work ok for publishing books, but could not play any audio or video in the book, making it fairly redundant.
We were excited to see that Microsoft Edge supported reading of ePub files in their browser, but they discontinued that service in October 2019. Another popular e-reader is Adobe Digital Editions, but we haven't tested our books on that platform.
For a while, we were keeping an eye on the Readium project, as they were building an open source e-reader for the Chrome browser. That seems to have ended now, but they do maintain a list of applications based on Readium that you could try (but please be aware, we won't support you to get books working in these apps).
The other option... PDF
If you don't need any audio or video to be played in the book, or any embedded content - that's to say - if your book just contains text and images, you could export the book as a PDF, which can be read universally on almost any device.