Every room with Smart Vents needs a temperature-reading device.
But remember, at least one Gateway Puck is required in a Flair home to serve as a communication hub for all your Flair devices over the internet. See Do I need a Flair Puck?
If you decide to use a smart thermostat and/or room sensor in a room with Smart Vents, please read this article to determine how many Gateway Pucks you may need for your system, as your installation may require more than one.
A room sensor cannot be used to control a mini split, window AC, or portable.