I have a very successful Nest Thermostat E and Heat Link. The 2 bed flat + studio is controlled by one central heating system and the Thermostat is in the flat.
Unfortunately the home away assist function, which is rather good, relies on motion near the thermostat so I thought I'd add a second Thermostat in the studio as my guests there don't walk past the thermostat.
You can't. Each thermostat comes with it's own heat link and I don't want to install two heat links onto one single central heating system.
Such a pity but hopefully you'll add this capability soon. If you did I'd purchase 2 additional thermostats so that motion is detected anywhere in the home.
Home Away assist is absolutely the money saving tool.. as it detects no-one is at home and regardless of the schedule and will turn on/off the heating.