When one of my two thermostats died, I replaced both with T9s. The installers advised me not to bother with the added room sensors - but despite the confusing instructions, I included them and they have helped to level room temps. What bothers me most is that they both measure 3 degrees lower than the actual room temperature. I have tracking thermometers placed in each room and they always read 3 degrees higher. True - I can adjust accordingly - but if this is a quality instrument, I shouldn't have to.
Worked great for a few weeks. It was awesome having control from anywhere. All of a sudden i was getting alerts every day saying the system was offline, then online, then offline again. I reset the wifi connection which didn't help. There have been no changes that could have affected it. Probably going to remove it and go back to a regular 'dumb' thermostat.