http://www.techradar.com/news/best-amazon-echo-speaker-the-lineups-dots-spots-shows-and-pluses-compared

Amazon's Echo smart speaker range started with just one device, the original Amazon Echo, but has expanded to now include five different devices. 

Now, as well as a newly revamped standard Amazon Echo you've got a beefier Amazon Echo Plus, and the budget Amazon Echo Dot.