I have a 2 wire (red and white) heat only thermostat that I’d like to convert to a WiFi thermostat that requires a C-Wire (Honeywell RTH6580WF) for ST integration.
Anyone know if something like this will work?
I expect this gadget will work on your 2-wire application, by its description and the circuit diagram on the gadget itself, which shows a 2-wire run from Tstat to the gadget located at HVAC equipment. FYI this gadget is made for hit-and-run installers that want a quick fix to old infrastructure.
You may have more than 2 wires run already. Using spare wires is preferable to the complication and lower-reliability of adding another device/gadget in the control scheme. If no spares are available then it may not be so difficult to run a new jacketed cable with at least 5-6 conductors. If you are planning to keep this house long-term, then IMO it is worth your while to add the wire to make the local and remote temperature control more reliable.
The Honeywell Tstat you have linked, … ummm, read all the reviews to be sure of what you are getting into. I don’t choose to depend on Honeywell’s network for remote control but I guess you have to trust somebody. FYI Honeywell is typically DIY-unfriendly.
Thanks. Unfortunately there are only 2 wires run. 
Also it is a very old house with no accessible crawl space below this area and old style lathe walls which is hard to run wires through.
I currently have two Honeywell RTH9580 thermostats with the Total Connect Comfort ST integration, so just figured I’d go with another cheap Honeywell WiFi for this. I assume the 6580 will work similarly?
Only issue I have with Honeywell TCC integration is the long lag between actions in ST and what actually happens with our HVAC system. Like up to 2 minutes delay.
-Scott