I've used Class Dojo before. The problem in China was that it was a bit spotty. Maybe your province will be better, but Chengdu was going through some political unrest towards the end of my time there, but when it worked, it really motivated the students.
One problem I had was that they would be so busy staring at their little avatars on the screen they would be off task. The way I worked around that was to turn the screen off and leave the little chime on, so they would know when someone earned a point, but they didn't know who. That trick created a sense of anticipation and competition which helped keep them focused. At the end of class, I would reveal the avatars to see who earned points in which category.