I have some pdf documents that I use from work, two column format with lots of tables and diagrams. I find the K3 to handle these documents very well. It is all a matter of preference I guess. You will not know until you get a device, or see one in Target, Best Buy or Staples.
The zoom feature built in to the K3 worked well for me as well. I was reading only a single column zoomed in, scrolling downward, and it was fine. It isn't like reading an ebook where you can change the font, line spacing and what have you, but it does work.