Andy comments:

I agree with 100% with the other poster, and you can pick up
a portable heater at a garage sale for $2 that will have exactly
the same efficiency -- 100%


But that being said, I personally prefer the oil filled radiator
types. They do not get hot enough to ignite anything, cost
about $40, and have a nicer look than some space age
gadget.

The types that use a fan blowing air over a hot coil can be
very dangerous if a shirt falls on them, or the fan stops for
some reason.... They will last a few years, then something
will go bad, usually the fan, and unless you want to take them
apart and oil the bearings to make it last a few more seasons,
they get thrown out. I have retrieved many, and fixed them,
but if I were going to buy one, I'd go with the oil filled radiator
type...

That type relies on low heat over a large large surface area
instead of very high heat over a small surface area. The effect
is the same --- to deliver 1500 watts into a room..... But it's like
comparing a 100 watt laser pinpoint at 10,000 degrees to an
electric blanket (also about 100 watts)..... A lower heat over
a wider area is much safer....

Andy in Eureka, Texas retired engineer