You do not need a smart thermostat to use Flair. Flair works with all thermostats.
For central systems using Smart Vents, Flair works in two ways to manage temperature: 1) redirecting airflow via Smart Vents, and 2) controlling a smart thermostat set point.
If you have a traditional "non-smart" thermostat, Flair will redirect airflow by adjusting Smart Vents. Flair will compare the room temperature with the room's set point to know when to open/close Smart Vents. Set Points are set using the Flair app or by rotating the Puck.
If you have a smart thermostat, like an ecobee or Honeywell, Flair will also be able to communicate with your thermostat to adjust the set point. This is an optional feature, controlled by a setting called "Set Point Controller'.