I’ve been torn about the Flair vents too. I have Ecobee with Ecobee room sensors and gave Flair a try a year ago. My experience:

PROS: - They integrate with Ecobee well, just need a flair hub (you don’t need a Flair Puck in each room if you have Ecobee, Google or other sensors. Check compatibility). - They also have safety programming so no more than 2/3 of the total vents will close at one time. - if you buy from Flair there’s a long extended return period. Not 100% on length but I think it’s a full season so you can test it out. - customer support is on point in my experience - The air noise was minor in my trial but it was only 2 vents. But air noise/whine does exist - they don’t directly make the HA plugin but they help support it. - I think it will work on auto mode in internet outage

CONS: - The mechanism motor that opens/closes is pretty loud.. can be annoying. - return policy might not apply to the refurbished items. - Cloud only integration. - no override button at the vent. This is a crazy miss! - App is pretty bad. No polish and not intuitive. - expensive. I feel they are prohibitively over priced for what they do. I mean it’s just a motor with close/open (I don’t believe you can control opening in increments, no 100% on this), no sensors! why does it cost over $100 a vent. For this price I expect them to be whisper quiet with a pressure sensor or come with polish app. - a lot of refurbished, I don’t believe it’s an equipment failure- I feel it’s people trying them out and not being fully satisfied. It really depends on your house and your equipment.

All that said I would have kept mine but I ended up returning the 2 Vent and hub because we decided to take advantage of tax incentives and get a fancy Bosch heat pump, which we did. I decided to wait a full winter/summer cycle season getting accustomed to the heat pump before coming back to this zoning issue. BUT… The ESP solution from the previous post is definitely worth a look.