It's very useful, if somewhat lost in its evolution. The script has two separate versions in the same package, more or less cross-compatible, but it's hard to figure why keeping the older version. This complicates the documentation unnecessarily.
According to documentation, the script doesn't completely support characters outside the ASCII scope. I think this information is probably outdated, but if it's true, it's a shame these days!
I found the choice of using points instead of milimeters highly disrupting. As a graphic designer, I shape my grids in milimeters, as points depend basically on the dpi ratio, which is hard to keep track of. Sure, we're on the web here, and the web is all 72 or 96dpi right? Still, perhaps it'd be better to set up dpi on the fly and measure everything with centimeters...
Still, don't take my criticism wrong: it works, and it's probably your best shot at designing PDF documents from scrath with PHP. There's much room for improvement, and the author did a great job improving it over time. It certainly saved my hide this evening! Kudos!