Take care that you know exactly what model you want & be sure that you have all the parts. I was warned that it's quite common there to pick up a really good bargain & then find that you have to go back & buy some vital component that they totally rip you off for.
It's also common for the sales people to tell you another item is every bit as good & try to sell you their preferred item, which generally is NOT a good bargain.
Make sure wherever you purchase is recommended by the HK tourist board.
You will find bargains as all the shops are tax free. It's good to be aware of the pitfalls & scams though.