PDF does NOT reflow, it uses zoom levels:
Fit page, fit width, fit height, 50%, 60%, 70%, 80%, 90% 100%.
If you zoom bigger than the actual screen, you can pan with the select key.
Actually, I prefer zoom over reflow, for keeping the layout intact.
On iRex iLiad, I can zoom any area I want.
Here I only can zoom the entire page.
EPUB DOES reflow.
For a unit that small and given the fixed zoom levels, I prefer reflow and will focus on EPUB.
And: About 90% of the cover's thumbnails in PDFs are defect, look kind of "distorted".