I'm a proud owner of a Xiaomi Mi Note Pro which I bought from honorbuy.com a few weeks ago. It's an amazing phone, so light, thin, and the build quality is amazing - it's better than that of my previous phone, which was a Motorola Nexus 6. I've encountered similar minor issues to the ones described in this article namely with the Google Services Framework needing to be installed, along with some elements of the native Xiaomi apps being in Chinese. Once you get the Google apps installed though there's no need to use the Xiaomi apps.
Some other pros I've noticed:
1) Weekly updates. From what I read the developers code away Monday to Wednesday, and then push out those changes to the weekly build which is released on the weekend.
2) The camera is the best I've ever had on a phone - better than my old iPhone 6 Plus.
3) The screen to phone ratio is great
4) The Xiaomi Piston 2 headphones which I got at the same time for US$15 are better than any of the Sony, Sennheiser, or Beats headphones I've had previously.
5) The permissions model is amazing - e.g. don't want that one app to have location access? You can just block it for that app, rather than either having to turn location services off which affects ever app.
As of yet I haven't experienced what would be the biggest con of owning a grey-import phone - warranty. Hopefully I won't ever need to experience it. Battery life doesn't compare to my old iPhone 6 Plus either... I'd become used to being able to go through a whole day and night without needing to charge my phone, and now with moderate to heavy use the Mi Note Pro dies at around 8pm or so.
If Xiaomi ever start releasing their phones in western markets and conduct their business in the same way as they do in China, I'm convinced after a few years their market share will be making significant inroads on the Samsung and Apple dominance.