I have one & am not impressed. I have it in my insulated workshop. Not particularly hot. Noisy. Costs a lot more in fuel than my radiant calor gas heater .to run. I get a quicker warm up time with my butane calor gas heater & as I do not spend hours in my workshop it is better using the gas. The requirement to use 12 V battery means that I need a battery charger fitted all the time, because the battery would soon go flat. That suggests that if on a boat one would need shore power to keep the batteries charged whilst it is running
I have 3 in sheds / Outbuildings. All running on red diesel or heating oil. for the last 2 winters. Throw away costs but still all running as good as my Webasto on the boat.