I have several of them. The heat they produce is quite good. The "cost saving" is negligible but still cheaper than LP gas. There is a problem that you need to be aware of when you buy them. They are built to last about 5000 hours, which is about 600 six hour days or nights depending on when you use them.
What this means is they are only built to last about 2 years with constant use, HOWEVER they are mindlessly EASY to repair. They only have essentially two working parts, the heat bulbs and the fan. The heat tubes are $15 each to replace (there are 3 of them in the heater) and the fan is $45 to replace if you do it yourself.
The company is VERY POOR, repeat VERY POOR at helping you when these things go belly up. You have to ask them where you can get replacement parts and finally they will tell you. Don't waste your time hoping they will "exchange them" because you'd sooner have a root canal without anaesthesia.
Parts are available from "The Next Energy Store" in Minnesota. The guy who answered the phone there talked me through removing about 38 sheetmetal screws to gain access to the "innards" of the thing and sent me the repair parts for two machines. Considering the cost of the two machines (~$650) the cost of the repair parts is a fraction of the cost to replace a machine that is "out of warranty" .
Repair is very simple and can be done with one screwdriver, about 6 small wire nuts and a little patience.
As I said, don't depend on the company to help you. I spent hours on the phone trying to get through their "smoke and mirrors maze" till I got someone who would tell me about the place to get the repair parts. AFter that it was a breeze!
Good luck with the heaters thought. They do work well and are quite nice to use. As for efficiency, the post above tells you all. There is no way to use 1500 watts and not pay for it. The advantage of these is the thermostatically controlled heat output. Honeywell makes the controller and it is a good one. That is where the efficiency comes from.