I tried the non-pro version, it mangles the formatting of the book, text size and position is wrong on the page and the UI.
It might be designed for text-only books? It seems to have every font option other than "display as intended." Might be useful for text-only novels where end-users messing with the fonts makes sense. I've got books like "The Complete Illustrated Guide To Table Saws" which has a lot of images and diagrams with text overlaid, so it needs to be displayed correctly, exactly as it was typeset. Applying font and size adjustments only breaks things.