In an offhand remark from a Xiaomi marketing type, it was intimated that this product had overtaken Nexus Player in total sales in the US and was approaching parity with Shield's takeup in international sales.
No response yet as to specifics.
Will update if/when details are forthcoming.
FWIW, Google has stated to the financial community that as of June 2016, 30 million Chromecast devices have been sold.
http://www.androidcentral.com/total-chromecast-sales-have-now-exceeded-30-million-units
Makes sense. The main competition is Fire TV. Shield is more of a niche market that expanded because of lack of choice. At $200-300 for Android gaming, it will get overcome by Xiaomi unless Nvidia makes a standard streaming box.
Fire Box is so Prime heavy that it can be less appealing for those who don't use/want Prime. Many, however, think it's the only device.
Nexus is discontinued.
Chromecast is different than a streaming box.
If Mi Box starts selling outside Walmart (whenever that contact ends), you'll see it being #1 until more Android Streaming Boxes enter the market. They have to expand fast and get their name out. The second nVidia or Samsung, or any better known manufacturers enter at $70-100 market, people will go for those known brands.
It's a short window Xiaomi has and they have to stay course.
The success or failure of most Android devices, however, depends on Google's software support.