Safety first: a diesel heater burns fuel on board. Combustion is sealed and the exhaust is routed outside, so the danger is not the heater working — it is the heater failing. A cracked heat exchanger, or an exhaust that leaks, corrodes or gets blocked, can push carbon monoxide into the living space. CO is colourless and odourless; you do not notice it. Have the unit fitted by someone competent, keep the exhaust sealed and terminated well away from windows, vents and hatches, and fit an audible CO alarm to EN 50291-2 — the part of the standard written for vehicles, boats and caravans, not the domestic one. This applies to every unit below, clone or not. The comparison itself is built from each maker's published specification and UK list prices; we have not tested these heaters.