The ADF allows multiple pages to be copied or scanned at a time without the need to replace each page in a photocopier or scanner. You’ll need an ADF if you plan to scan common-base documents—especially documents that are more than one or two pages long.
The flatbed scanner can scan anything that can be placed on top of the glass. You need a flatbed for photos or perdiplined materials, bound materials, and 3D objects. Usually a flexible lid allows scanning a thick document or even a book.
With more input trays you can hold more paper also have the option of using paper with different colors.
We consider the thinner chassis to be better because it makes the product more compact and easy to carry. Thinness is a feature highlighted by many mobile device manufacturers, but it’s important for a wide range of products.