I recently purchased the "New improved" DPMS wrench from Midway. This is the model that has the enamel-like, speckled coating. It's on the way back to Midway because one of the barrel nut protrusions broke off. As I was in the middle of my project when this happened, I located another wrench at a local gunshop. This was also a DPMS wrench, but the older type-without the coating. This older-style wrench performed very well and enebled me to finish my project. My thinking is that the barrel nut protusions or "teeth" on the new-improved wrench are weaker. In order to conform to spec, the teeth on the new model must have slightly less metal thickness (as opposed to the older model) in order to to accomodate the additional thickness of the enamel coating.
Nonetheless, if you will be installing free-float forearms or doing any kind of barrel replacement, I would highly recommend, in addition to the aforementioned standard armorer's wrench, a free-float wrench by Yankee Hill Manufacturing (YMH). Unlike the 2 barrel-nut teeth found on most armorer's wrenches, this model features 3 teeth, which will provide a much more secure fit and dramatically reduce the chances of damaging the barrel nut (something that did happen with the newer DPMS wrench).
Hope this helps.
Greg