Very good, and thanks for opening this thread!
I am using this integration, and even though this early functionality is quite restricted it is working really well. I have a node-red workflow to monitor and control the air quality using a PI controller that I have mentioned elsewhere. I know it is possible to add CO2 sensors to the Flexit, but I already have 2 external CO2 sensors. My solution cannot control the fan speed directly, and uses the preset modes instead, so it will not be as good as a built in CO2 sensor, but I have it working quite well, I think! The example in the figure shows that the load (calculated by the PI controller) follows the CO2 concentration well and I used this to change the preset mode appropriately.
More on my implementation here. It will be updated shortly as I have made some considerable improvements since writing the article.