In all probablity you are just getting used to photofocus and each eye is compensation hence the switching effect.
As long as your gaze remains relaxed you are probably using parallel vision. If you experience eyestrain then you are probably crossing them. The key is to relax.
There is a comprehension test for the Natural Brilliance book that came with the course in the manual. Other than that you might want a book that quizes you at the end. The end result for a book that is fully gelled for you is comprehenion to a level that you are accustomed to gaining from regular reading. It should be the same or better. In other words you should be able to talk about the book as well or better than you normally do.
Alex
