Why I don't use ebook creation apps
(but you might want to anyway)
Many years ago I built my first website, using Dreamweaver. It was Version 8, I believe, back when it was still by Macromedia. The website was very basic, the program very complex. It suited my needs at the time, and had plenty of potential for expansion...if I wanted to learn how to code a complex website, that is.
So instead, when it came time to add a store with shopping options for buying print and ebooks to my site I switched to Yahoo SiteBuilder, since Yahoo were the top web hosting service at the time, and offered a simple add-on shopping cart package (for a fee, of course). But since Yahoo used their own proprietary code for web page layout and functionality, I had to rebuild the site from scratch, being unable to import the current site and build on that. However, after much tedious effort (not to mention learning an entirely new software interface) it resulted in a nice website that filled my current needs...for a while.
But web technology moved on and Yahoo did not. Eventually I wanted to upgrade my site to include some of the nifty new features made available by HTML5 and CSS3. But that could not be done in Yahoo.
So I moved my site to another 3rd party web platform...and built it all again from scratch, since Yahoo's super secret code matrix could not be transferred to another platform.
That new 3rd party service went out of business within a year (Yahoo has fared only slightly better treading water).
So once again I started over and rebuilt the site from scratch (that's four for those keeping track). This time I decided to use the popular "open" platform Wordpress, with its highly customizable theme-based structure, thinking it would be more "universal," since there were seemingly endless theme and expansion packages available for it.
But Wordpress proved to be slow and balky, crashing frequently and losing data with nearly every update. And because all but the basic layout functions are handled by adding third party plug-ins for each new feature, these tended to conflict with one other more often than not (not being tested for compatibility with anything but the base platform), causing features or entire sections of the site to malfunction (or not function at all), and crashing the site when any one of them were updated, even locking it up in a perpetual feedback loop on more than one occasion - a cycle which could only be broken by deleting one or more of the expansions, which naturally took all of my data with it.
Moreover, due to the very nature of this "plug-in" methodology, the site was once again not exportable to any other platform. So yet again I was faced with the seemingly inevitable task of rebuilding my site from scratch.
So after building the same site five times, I am now back to where I started, using Dreamweaver to build all my site content with universally recognized web code based on standard HTML and CSS. It is infinitely expandable, limited only by my time and willingness to learn, and can be transferred from one hosting service to another as I see fit. And it's the best site I've built yet. More importantly, the underlying code can be read and edited using any standard text editor. I can fix it if it breaks, and add new features as I learn to implement new code. If I see something I like on another website I can view the source code in my browser and see how it was done. I'm not limited by what the software can do, but what I can do.
You might be asking yourself at this point what this has to do with ebooks.
An ebook is, in essence, simply a portable website, designed as fixed or responsive page layouts, and based on a subset of the very same HTML and CSS that websites use. In general, if you know how to make a basic web page you can make an ebook too. You just need to learn the specific bits of code that makes the ebook work, and the rest is left to your imagination.
And best of all, the only thing you really need is a text editor.
The very same issues that plagued my web building experience for so many years also apply to building ebooks, so take heed. Programs that build your ebook for you do so by using their own proprietary code that often can't be understood by mere mortals such as we (unless you have the patience of a saint, or the wisdom of a god, which I do not). For example, they change the names of all your input source files, so that rather than having page23overlay2.jpg, you might find img000172.jpg instead, in your new HTML page called split0000159.xhtml. Good luck finding the correct file for page 23. Or the images it contains, if you happen to want to change one.
This is made all the worse by the fact that all of your carefully labelled CSS entries will have been changed in just the same manner, so that your styling instructions for #page23panel1 is now called data-app-amzn-ke-created-style0126, or some such nonsense. And more than likely all of your neatly organized HTML will be run together in an endless stream of code. Needless to say, this is not helpful in the least.
Unless you're a machine. And a very specific machine at that.
This applies not just to Amazon's proprietary Comic and Kids ebook creator tools, but also in varying degrees to iBooks Author, InDesign's ebook export function, and ebook editors such as Calibre and Sigil. The code they create can only be effectively read by them, thus locking you into using that same platform for all future updates to that file, until such time as their usefulness runs out, they become incompatible with your now-outdated file (or operating system) after an update, another software offers better features, or the company goes out of business.
Then you'll face the same dilemma I did building websites.
You'll have to build your ebooks all over.