you need to invest over a mil US$ to be eligable to get one of those plate but the waiting list is also very long which leads to more money being spent on the govt officials (dinners/ktv/massages/spas). once you are approved your factory or office usually gets two plates (depending on how much money you splashed out on the officials). you keep one and you sell the other (going rate is 700K HK$$).
Dual Plates:
Pros: Can driver across into China and explore around
Cons: your car value will drop like a brick