Well if he's played with Steve Vai then that must mean that is he one very talented drummer but my biggest concern for Dream Theater since Mike Portnoy's departure has been and continues to be all of the other things Mike did for the band since he wrote a large chunk, if not the majority, of their lyrics, handled half of the production for their albums, and numerous other backstage things. Now they all are hard working guys who I don't doubt can fill in those rolls but I just wonder how different it'll be still....
Oh and here's a pic of Mike Mangini with the rest of Dream Theater: