According to Harmony's website Smart Si devices are compatible with the Hub. I just want a cheap thermostat that I can start and end an activity within the Harmony app. Ecobee Smart Si legacy thermostats seem like they would work.
Welcome to AVF. It is mainly a UK and European site and some products such as Ecobee thermostats are not widely available over here, so it is unlikely that you will get too much of a knowledgeable response.