The eBook versions are tested and known to work on:
- Linux, Macintosh, and Windows computers using Acrobat Reader or other PDF readers
- Apple iPads (preferably with Goodreader*)
- Android tablets with PDF readers
- All current Kindle models
- All current Nook models
Due to the proliferation of devices, I can't test and guarantee compatibility on other devices, however there's no reason why they shouldn't work on other devices that have PDF readers, even smartphones with PDF readers. However, smartphones is one category I'd discourage: while the PDFs look good at tablet size, the small screens of most phones will have you squinting and scrolling a lot. Still, if your phone has a PDF reader on it, the files should work.
*Why do I specify Goodreader? Because it has better memory management than the built-in iPad support for PDFs, plus allows commenting and other features. My Complete Guides tend to be very large files, so memory management on restricted memory devices (tablets, eReaders, phones) is something you want to pay attention to. The original Nook Color was somewhat problematic in memory management for PDFs, too, though this has improved in the latest release.