I’ve found that the easiest way to do this step is to store (and output) your project files in a cloud storage space like Dropbox, then install several reader programs and Dropbox (or whatever) on a mobile device like a tablet. You can navigate to each of the book files in Dropbox, choose to open them in the appropriate program (the Kindle reader for Kindle files, something like the Kobo, Nook, or iBooks app for all .epub versions), then go through them that
