Why I write on document scanner
Where portable scanners drop the ball a bit is with regard to the quality of the image. All things being equal, a larger desktop scanner will give you a much clearer image than a portable scanner. Nevertheless, they are sufficient for most casual uses, and their small size and portability makes up for any deficiency in image resolution. If image quality is of more importance to you, you will want to look into a portable scanner that has a high dots per inch or dpi image resolution. Make sure to offers at least 48 bit depth image quality if you're particularly concerned about getting the best images possible.