The failure stories I have heard convince me these are not fail-safe devices. If the thing shuts down in the winter and doesn't restart correctly, and you are away, you could come back to frozen/burst pipes. (Probably hasn't happened yet, but the failures have happened, so it's likely just a matter of time.)
So I would only use one of these paired with a conventional thermostat serving as a safety net, in case the Nest fails. But then I resent having to compensate for a manufacturer that cannot be bothered to build the failsafe into their own product in the first place.
So I would only use one of these paired with a conventional thermostat serving as a safety net, in case the Nest fails. But then I resent having to compensate for a manufacturer that cannot be bothered to build the failsafe into their own product in the first place.