The best MP4s or MP5s for e-books were usually tablets or smart phones because they had powerful e-book reading functions such as built-in reading lights, expansive storage, and support for multiple e-book format. However, if you need a device specifically for reading e-books, some MP4s or MP5s are also good choices. Some MP4 or MP5 devices also provide additional reading functions such as reading aloud, annotation, bookmark, etc. These functions can provide a better reading experience. The choice of equipment depended on the specific needs and budget.