I’ve been testing one of these for a couple of months now in my workshop. They are pretty safe as long as you follow the installation guide. The pump is a dosing pump, not gravity fed, so can’t run away, any electrical or cpu failure just kills or stalls the pump, the glow plug manages about 100w enough to vaporise the diesel, but not enough to heat the alloy casting of the heater. As to the heat out the exhaust, once you are upto temperature and the thing throttles back, the temp falls away and you can hold the silencer. I am still waiting for the unit to soot up and fail, parts are cheap and the heater mesh can be fabricated. I run red diesel and for a 2kw unit it costs me less than £1.00 a day for heating. I use the heater 6-7 days a week for 8-10hrs a day. I did insulate the workshop roof and door with silvered insulation from Screwfix and this made a huge difference. I only need 10℃ To be able to work, but the added benefit is, the heater has dropped the moisture that was present in the shop.
I might add, DON’T drill a hole in the tank to fit one of the fuel fittings. Drill the tank lid and pass the fuel line though and add a clunk to sit at the bottom of the tank. My tank is fitted so it stand vertical, I have x2 20ltr Jerry cans for fuel and decant into a portable 10ltr can. It’s easier to fill the heater tank, just use a funnel.