When you envision billionaires living extravagant lives, a man from China who got rich by selling medical devices is probably not the first thing that comes to mind. But Xu Hang, co-founder of Chinese medical device manufacturer Mindray Medical, is on a real estate buying spree that would make a Saudi oil magnate blush. In the last few years, buyers connected to Xu have bought $250 million worth of luxury estates around the world.