That's interesting. So you've built your own HTML to PDF converter? Can you provide an example (a screenshot, maybe) where your version excels against an existing solution?
Flying Saucer excels against the alternatives I looked at in a few ways. First, Pandoc's built in PDF writer uses a LaTeX intermediary which doesn't support anything that web writers have come to expect. Second, the other tools were webkit based which variously didn't support the page media spec, didn't support embedding fonts, or both. Others were custom one off of desktop tools that wouldn't work how I need for Docverter.