Just give it a try
There is an almost religious debate here where some people prefer the K3 (Keyboard), some the K4 (non-touch), and some the K5 (Touch). You will essentially only start the 800th discussion about who prefers what, and get subjective comments about how the K5 doesn't have physical buttons, the K4 doesn't have a keyboard, and why the keyboard on the K3 is useless.
Objectively, the K3 is still a good reader if you just want to read books. As far as actual reading is concerned, the only thing that it lacks (which newer models provide) is support for KF8 books (required for RTL languages like arabic or hebrew, and providing better support for complex book layouts, like for technical documents).
Again: just try it. If you don't like it, you can still buy a new one.