Trouble with it is that they often times don’t include a ground wire. All the thermostat does is connect the power wire to the given function wire (like “fan on” or “heat pump 1 on”. I am not an expert but having installed a number of thermostats in a number of homes, all the manuals talk about the ground wire being rare and I have never seen one. If you are lucky you might have an unused wire that you can find a ground for, but I have only seen that once. Somehow when houses are wired it seems the HVAC people are very efficient with using the exact right number of wires in a single cable.
I wasn't a fan of messing with the thermostat housing but just now after pulling it off, I think my thermostat isn't anything fancy like that, just two black load and two red line wires. It's also important to note that my thermostat connects to baseboard heaters, not an HVAC system.
Even ones connected to fancy heating and cooling systems aren’t that complex and instructions are usually spot on. A simple heating system like you describe is, well, simple. Connect wires, get heat. I’m sure you can figure it out.
That only works if they didn't staple it to the wall or bury it in spray-foam insulation. I ended up having to run a new one but was lucky that the floor-board was under the garage. I ran a piece of cat5e as well in case there is ever an option to get a thermostat that can use it.