Logitech has recently changed the names of their remotes/hubs. Please see below for new naming information:
Harmony Smart Control = Harmony Companion
Harmon Home Hub = Harmony Hub
All of Logitech's hubs can be controlled using the Harmony smartphone app. All of the hubs are also capable of connecting with other smart hubs such as SmartThings, Alexa, Lutron, and Hue.
The Harmony Companion/Smart Control comes with the Harmony hub and the RF remote. The smart remote works through the Home Hub and both of them require an internet connect in order to function.
This video is a review, comparison, and overview of Logitech Harmony Smart Control, Companion, and Harmony Home Hub.