I haven't ordered an Arduino from China, but buy electronic components and boards from Chinese sellers on ebay, never had an issue. Remember that 100% of electronics that you own was manufactured in China and an Arduino is not that complicated (an atmega, a power regulator, a bunch of headers and some misc resistors and such.
However shipping will take some time. To the US it's anywhere between 3-6 weeks. If you need something within a month, order locally.