From talking to my colleague with an ecobee, that's not the point. If the ecobee detects a big swing between the two sensors, it'll run the fan, but not the heat/cool. That balances the rooms. It makes sense.
Yeah, I get that. I was speaking generally about what that does. That's how Ecobee works, but even still I'm sure it's not perfect. (I haven't tried it myself, just similar types of setups).