My personal experience with Dr. Ang was not good. He lead me through several missed opportunities in curing my lung/cough problem, which ended when I was sent to the emergency room the next day after visiting him. And he didn't reply my message until the following week.
But, it is an issue of how efficient can the doctor give a correct diagnosis to your sickness. If after visiting a specialist 3 times without solving your problem or seeing improvement, you should probably go back to your primary doctor and ask for a different referal.
Pros: patient and nice.
Cons: not very smart.