Browser print-to-PDF often mangles layouts, cuts off content at page breaks awkwardly, or includes navigation bars and ads you didn't want. Converting an HTML file directly gives you more predictable, cleaner output for archiving or sharing.
Simple, well-structured HTML with inline or linked CSS converts most reliably. Heavy use of JavaScript-rendered content (things that only appear after a script runs) won't be present, since the conversion captures the static markup.
Yes, linked and inline CSS styling is rendered faithfully in the output PDF.
Currently you can upload an .html file directly; URL fetching is coming soon.
Yes, as long as image paths are accessible relative to the HTML file.