For most homes, yes. A properly fitted smart thermostat makes two real differences: it holds the room temperature more steadily than a basic mechanical stat, and on modern boilers it can modulate the flow temperature based on the weather — which is where the efficiency gain actually comes from. The phone app is a nice-to-have; the gain is in the control. We fit controls that talk to the boiler over OpenTherm or the manufacturer's protocol so the system runs as efficiently as it's capable of, rather than simply switching the boiler on and off. If you're already upgrading the boiler or the wiring centre, adding a decent set of controls at the same time is a much smaller job than retro-fitting them later.