As I said, it's very small, for PDFs that have formatting that can't make use of reflow or conversion to epub of that matter. That's pretty much every PDF with tables in it.
You could slice it up more, get rid of the unnecessary page borders for example to get a bit of more size out of it - the reader has a zoom function but it's not particularly useful as it takes too much time to adjust and sometimes plain doesn't work as expected.
Still if you have to rely on PDF a lot you may be better off with a tablet after all. Even if it doesn't have a larger screen or higher resolution, pinch zoom and realtime responsive display will do wonders for usability.
I highly recommend this ereader - for reading plain text ebooks, and maybe comics. It's actually very good with pictures as long as they come in the readers resolution.
PDF just sucks for any kind of reader. It might get the job done if need be but it's not something you do for comfort.