My previous boat had an old propex heater on it, presume it was similiar to these units (never looked at it that closely). Seemed to be more reliable (less voltage sensitive) and way less smokey (i.e. no smoke) than erbawatsits on friends boats although much less heat output but may have just been a low output unit.
Not worried about having gas around if its installed properly, as well as the gas heater, the boat had a gas powered fridge that was on continously. The boat is now circa 30 years old and hasn't blown up yet.
I fitted a Propex in previous diesel engined boat very quiet very effective.
Puchased from Calor Gas Centre Southampton just after Boat show where they had one on the stand actually connected & running (happily paid boat show price) .
Current diesel boat has an Eberspacher.
last seasons Thames accidents involving gas and petrol would suggest that proper inspection maintenance and caution when re-fuelling are mandatory.