With the recent changes in the Nest API, I have been looking for an alternative... Rather than go with another cloud-connected device, I opted for local control only. Of course, using Indigo with the reflector provides the cloud connection for remote visibility & control.
Here's a quick note about my experience with the Honeywell T6 Pro Z-Wave thermostat. This is also branded as the "Honeywell Intrusion TH6320ZW2003" in case anyone is searching for specific models.
So far, this thermostat is working quite well. Setup was straightforward and inclusion with Indigo was easy. The only snag I ran into was trying to include the device with encryption. Indigo could not sync until I added the device with encryption disabled (using Aeotec Z-Stick Gen5 interface). I've had other issues with using encryption, so I don't think this is specific to the thermostat. Eventually, I'll try to dig into why this isn't working as expected.
Once included in your Z-Wave network, it is important to know that the thermostat disables all local scheduling. It assumes that the Z-Wave hub is the master and goes into a slave mode. This is exactly what I was looking for - let Indigo be the brains here. It might not be what others expect, since it is different behavior than the Nest.
The only feature I haven't found a way around is using the "away" setting on the thermostat from Indigo. It would be great if there was a way to set this via Z-Wave. I've been able to get close using Indigo with a combination of the auto heat/cool mode and other occupancy detection (phones). The challenge with this approach is ensuring that the unit returns to the correct mode when people are at home again. I'm not sure when the thermostat engages the "away" mode, so hopefully there are no conflicts.
Anyway, if someone is looking for a reliable Z-Wave thermostat, this one seems to be a good choice. If there are other tips and tricks for this model, I'd be glad to hear them!