Hadn't heard of this before. looks like you can use it to print web pages without all of the irritating crud and it works on voluntary donations. Sounds like a good thing.
The references are still click on and go and in this particular case you get a reference library of the Napoleonic wars in a oner. I find it a very useful tool
Incidentally, for Napoleonic buffs, that link is a good one to bookmark even if you don't make a PDF