I actually use the linked supplement for an Avatar 4e campaign I'm currently running. There are some balance issues with some of the classes, but they each do a fantastic job at representing the various benders.

One of the problems with using reflavoured official classes is most of your results aren't going to be able to manipulate their element outside of attacks (unless you house rule or the players do some serious item digging...or if one of them is a wizard), however the supplemented classes take care of this, giving each bender an at-will ability to do exactly this.