Flair works with all thermostats, so you don't need a smart thermostat. If you have a traditional thermostat - or will not be integrating your smart thermostat - Flair will work alongside your thermostat, using it as a "non-integrated thermostat".
When using a non-integrating thermostat, Flair will be able to tell if the system is heating or cooling by reading the duct temperature, and then open and close Smart Vents as necessary to keep your rooms in a comfortable range. You'll use the Flair app to define a home set point, create a schedule, and set Home/Away.