I just took down from the wall my second pair of Insteon thermostats. I'm not getting a third pair. I'm pretty sure I know what went wrong with them - each time we had a power outage, presumably with a power spike at the beginning and/or end, the two thermostats would die - the LCD screen displaying giberrish or zeroes and the device non-responsive to the buttons. Resetting didn't help. At first, I thought it might be a fluke, so I bought a second pair. But when they went out simultaneously under the same circumstances, I have to conclude that they have no protection against power surges.
I had high hopes for these. I went to the trouble of running 5 wire thermostat cables from each of my condenser/heater things to replace the 4 wire ones that were there, in order to run these things. I had never gotten around to coding for them - it was a little more complex than I had hoped, and I never was able to put together the time and focus to break through that hurdle - I think it's just that they use extended Insteon messages instead of basic ones, and I haven't yet written the code to support that - lame excuse, I suppose. But the power spike vulnerability seals their fate.
Which leaves me... where? Vendor-connected thermostats seem to be ruling the market - Nest, for instance - but as I mentioned earlier, I'm steering clear of vendor-connected devices where I can, and this is a situation where I would rather have dumb thermostats (like I do right now), than compromise on that principle.
Problem is, I suppose, that the vendor connected thermostats have been going so strong that there's not much market support for local-only smart thermostats. There may be some that are zwave or zigby, etc. (it's true that I have not yet coded any support for these more modern protocols). But I'm thinking instead about keeping the dumb thermostats and wiring those 5 wires (or some of them) to a raspberry pi that also has a relay shield with another 5 wire cable which actually goes to the condenser/heater and controls it. The dumb thermostat would appear to continue to operate normally (important for certain family members...) but in fact would be simply sending its information to the raspberry pi which would in turn echo the commands using the relay shield - as well as doing other things I suppose. I'll try and post updates on that project.