Are the portable electric fireplaces any good?

I had considered buying a portable fireplace, an electric one. Has anyone had experience with these, in comparison to just a standard electric heater? I know that the fireplaces are essentially heaters, but are they just as effective (all things being equal, of course). I have a room that is around 130 sq. ft. My brother enclosed it last year (it used to be just an open back-porch), and he put in heating ducts, but it is still chilly in the room. I'd like to invest in a good heater, but not spend more than $100 on it.