I have 11 Keen vents in my house and use this driver: Keen Smart Vents - #94 by kahn-hubitat
and I use this to control them locally with: Keenect Lite (Release) - 
Get Help / Integrations - Hubitat
There is a fair amount of information in these threads to help you get things working. I have a strong zigbee mesh and have no problems with my setup. I get about a year of battery use for each vent.
I have been using Keen for 3+ year. I am very happy with them. They have helped greatly to balance the temperatures in my 3000 square ft house 3 floor house.
They were starting to go out business then and you could not buy directly from them. I bought all of my Keen Vents off ebay. Most of the Keen Vents were manufactured between 2015 - 2017, or at least that is all I have seen. Just make sure the seller confirms the battery compartment does not have corrosion. A couple listed as "new in box" had old batteries leaked and ruined them. I was refunded so no big deal. I have never had any issues with ebays money back guarantee.
I have 10 extra Keen vents in reserve to replace any vent failures and over the years I only had to replace 1 of them. I have had the time to watch for good prices on ebay so it's not like I paid full price.
Search for Keen or Flair and you will find good information for both.
