The obvious question about this is simple: why get this when there's a ton of free graph paper online? Or even just a sheet ripped out of a spiral bound notebook? The answer is equally simple: for a few shekels you get a pdf that is formatted a notch better than the free alternatives. If you're running games, you might as well keep your notes in a better format. These have the simplicity and flexibility of planner pages, and are well suited for the purpose they are intended.
And in the end, with a simple product like this, that's the best possible praise: they fit the task better than alternatives.