Good, but not great.

The good news is that the resolution and slightly larger screen size make PDFs with small fonts and fine lines much easier to read. You won't be suffering through fine details being lost due to antialiasing artefacts. This means that the subscripts are visible on equations with small fonts, while lines are sharp on things like graphs and circuit diagrams. That's true even when the page is zoomed out to fit the screen: it is very readable, albeit it is very small.

The bad news is that the PDF viewer is bare bones. It will scale the pages and allow you to scroll around those pages. The scrolling is fast, but only because they don't bother clearing the screen between refreshes. Turning pages while zoomed in is awkward since you have to scroll to the edge of the page first, then tap. It doesn't reflow text, nor detect columns, nor do anything else that would make reading technical documents pleasurable -- but it does get the job done. Compared to my prior experiences with PDFs on eink based readers (Kindle 2i and Kobo Touch), it is a significant leap forward.