The Amazon Echo has sold an estimated 3m units in the US

"Many products seem fascinating to geeks and techies but fail to catch on with wider audiences, from dual-booting smartphones to smart blowdryers. However, the Amazon Echo seems to be a real hit, with a new report from Consumer Intelligence Research Partners estimating the retail giant has sold 3 million of the smart speakers.
The Amazon Echo, which uses the cloud-based AI Alexa to answer queries, control smart home devices and play games with users, has seen plenty of support from Amazon, with new abilities added almost every week. But consumers seem to have seen the value as well."

Source:  Geekwire, 6th April 2016