I got 3 sensors as well. For me, the killer feature is the ability to auto switch heat/cool, something my old 14 yo thermostat was lacking. The rest is a none issue, mainly easier programming etc...
AFAIK 4th gen Ecobee biggest "improvement" is deeper Alexa integration, which I am interested in, as much as royal penguins interested in ice cream.
Btw: Installation is not hard, but this site was helpful to figure out some details:
https://www.stevejenkins.com/blog/2014/09/how-to-install-an-ecobee3-smart-thermostat/