Geneva, Manila or Hong Kong airport for Classic Moonphase Ultrathin purchase?

I'm pretty much decided on a Classic Moonphase Ultrathin.

I live in Geneva, so can obviously pick it up here. I have an upcoming trip to Manila and will be transiting through Hong Kong airport for about 2 hours on my return. My initial thinking is I am best off purchasing in Geneva, but is there any possibilty I could get a significantly cheaper price in either Manila or Hong Kong airport? Any worries about authenticity in either setting?

Thanks for comments.