Dr Duan is a very nice person. I spent an hour talking to him, asking a bunch of questions, when I first visited him. And he really took the time to answer all my question. I had several fillings with him already. Everything seems well. His checkup *seems* more thorough than other dentist I've visited.
The only complain I have is about his relatively higher cost, because supposedly he's a specialist, and therefore can claim higher prices from you and your insurance.