I think you can get good deals in Sisley products. There is about 15%-20% discounts on all Sisley products. For some new products, such as "All Day All Year", the price in the duty free is about NT7,400 and is competitive. I`d also like to recommend the products of Jurlique. The prices in the duty free shop in CKS airport are much better than they are in the department stores and the duty free store in HK airport.
I am sure there are discounts on products of other brand names, but I didn`t pay attention to other products.