It fit perfectly in my previously installed Honeywell thermostat. The instructions for ISU's were very helpful and with a little research, I was able to properly select and set the thermostat advanced menu options. It performs well and given the main reason I purchased the WIFI version, which was to support changing the settings remotely, I will save 3+ times the cost in the first year of use.
Works great from remote locations. The geofencing turns my air to the desired temperature before I get home. Customer service was very friendly and helpful.