This is interesting. I have had Nest thermostats for several years, and overall I think they're great, but I have definitely felt the need for remote sensors (our upstairs thermostat in particular is in a really bad spot). A couple of months ago I seriously considered getting an Ecobee, but I read a bunch of reviews that complained of stuff like unresponsive touchscreen, bad UI, etc. The main thing I love about the Nest is that the UX is very simple, and works well. Anyone in the house can use it without instructions, and it feels like a thermostat, not a slow Android device or something.
Did you find those to not be issues? Definitely most of the reviews were good, so maybe it's just isolated people having problems. But I couldn't tell if it was that, or more that people either aren't as picky about UX as I am, or they didn't have another point of comparison... I'm very open to re-considering them if someone can convince me this stuff is a non-issue, because the remote sensor would certainly make our system work better.