It's a nice class AO, since it's becoming effective for players with level 30+. They made a good decision with this class. I think, in the future, they should release more combination classes (between other "base" classes, like AO).
First of all, don't say "This class is good". You must say why and stuff like this. Second, yes it's good. I made a TSS vs DBSK in farming, and i must say, DBSK is more effective than TSS. I entered a room with 5k HP monsters (/earthstorm) and beat them up very fast. It's easy to use, if you know the right combination and timing, and has some great advantages. The double AA is beautiful, and both mana regeneration and HP regeneration makes this class capable of soloing and it's not bad in PvP.