I'm not sure what we're meant to be comparing it with. If with other ereaders, then I can't because my K3 is my first and so far only one. My only comparison is with dt books.
Easy to hold for reading in bed.
Small, lightweight and portable (fits in my handbag).
Stays open when I want.
Contains a library for my frequent travels.
Low tech (from the POV of the user) so very little to learn in order to operate it.
Tied to my Amazon account (where I have bought majority of my books for ages).