The pain in there is that every time you want to have a PDF generation system, you have to do the same stuff, it's not "complex" at all, but it definitely takes time, whatever the technology you use. On my experience, having ten thousand PDF generating at the same time was a very high load for our infrastructure and the cost was enormous, that is one of the main thing I'll focus on today : the scalability of it. It also depending on the way you create your template, hard coded with pixels or HTML!