Adam Jury noted over on FB that the licensing requirements may make it difficult to use within the RPG market. The terms of the tool state:"If you charge a fee for any book or other work you generate using this software (a “Work”), you may only sell or distribute such Work through Apple (e.g., through the iBookstore) and such distribution will be subject to a separate agreement with Apple."
I doubt that will be an issue.
There is, of course, the possibility that one doesn't charge anything at all to get their work out there into the ether. The tool allows you to distribute either through the iTunes store or on your own.
For more information on this, see The Writer Beware Blog. The problem with the license is that Apple can reject your book for distribution through their site, at which point you are out of luck.A better option is to use Pandoc to translate Markdown-format text into an ebook. It's not WYSWYG, but it's pretty simple and free (not just in terms of cost, but in terms of onerous licenses, too.) Can't live without WYSWYG? Use OpenOffice, save as HTML, feed that into Pandoc to get Markdown, then convert to epub (you can probably do the conversion in one step, but personally I'd rather have that plaintext Markdown version as a universal source.
Talysman: the point is having access to the Apple ecosystem and its huge volume of customers. You can always publish your work in multiple formats.