This is only my opinion, but the heating element and fan are totally enclosed in their own inner metal box, and that is totally enclosed in the upper metal cabinet of the fireplace. ANY electric heater can have a fan malfunction, and most of the regular electric heaters do not have the fan and heating element double enclosed. Yes, a simple thermal fuse might be desirable to add to the heater circuit.
I think we have heard much, much, more on RV forums about refrigerator fires than about electric fireplace fires. In fact, I haven't heard of one electric fireplace fire. But I am concerned enough about RV fires to have spent $270 and installed a self-deploying halon fire extinguisher in my refrigerator compartment, along with re-enforcing the rubber propane flex line connecting the kitchen slide against road debris breakage. I have also rebuilt replaced every insulation displacement 120 volt electrical outlet in my rig with standard screw connector types, as a protection against fire, and electrical bad connection problems. I also have an (apartment-type) escape chain ladder in the bedroom in case of fire.