I had a 2nd generation nest thermostat that didn't support remote sensors. My thermostat is downstairs and before it gets to a target temp the upstairs is very hot. The T9 with a remote sensor has made everything more comfortable. It works really well. The app is nice too.
I installed this thermostat to replace an American Standard ACONT624A thermostat which controls a 2 stage AC and 2 stage gas heat. It was very easy to install. It you have a multi-stage system you will need to go into the configuration menu to advanced setup and set the number of stages you have for AC and heat. I also installed one sensor on the other side of our home which helps with detect and direct the desired range of temps. Very easy to operate. Works well for us.
The thermostat works fine but the app for control needs some serious work. The geofencing fails to work properly sometimes. I have also had the thermostat get stuck in away mode a few times even though the app geofencing says home. The only fix was to restart the thermostat.
It was easy to use, that's #1, but it is also easy to see. The bright backlight is excellent. It also easy to read and the selections make sense. Last, but not least, it works!