Comment by jcgrillo
6 hours ago
The Honeywell thing I bought on amazon turned out to not be analog after all. It's got an Atmel Atmega something or other in it. It obviously can't connect to the internet through its 24VAC 3 wire interface but it's running software I can't inspect and therefore assume to be completely riddled with bugs. It's going back to be replaced with Whites-Rodgers Emerson unit.
Yet, it's common. They typically are drop-in replacements for classic mercury switch thermostats. Mercury is not available anymore (for a good reason), and gallium alloys wet almost everything.
Bare bi-metallic strips don't work as well because contacts tend to get oxidized and/or stuck. They are also a pain to calibrate.
A small microcontroller with a relay tends to be more reliable.