Inline duct fan

Wanting to install a 6" duct booster fan for an AC/air handler in attic with flexible ducting. Do I have to wire to a duct stat? Can a duct stat be used in attic and/or with flexible ducting? If not, how else can I wire the fan to operate when air handler/AC runs?

Any help is always appreciated!

Sail switch

My opinion is they don’t work for beans in flex duct. Put a short section of metal duct and re-connect the flex to both ends and it will work proper. As david so breifly stated a sail switch works fine but it can also be wired into the blower control when ever the blower starts the inline fan starts also very simply process

Pressure switch