The Optimus H-5210 receives consistently high reviews from consumers who have bought this heater. That is not to say it is perfect; but we'll get to that in a minute.
The heat source for the Optimus is two quartz infrared tubes. This allows the choice of two heat settings from a simple Hi/Low switch. The low setting powers one tube equal to 400 watts while the high setting turns on both tubes for a combined maximum power of 800 watts.
More than a few users of this heater claim the 800 watt output equals the heat output from more powerful 1,500 watt heaters they have owned. And with the heater set on 400 watts, it works well as an office heater when placed near a work station or desk. Since infrared heat warms people and objects rather than the surrounding air, a cold metal desk quickly becomes comfortably warm.
The Optimus H-5210 in not only inexpensive to purchase, it's also one of the least expensive electric space heaters to operate. Assuming an electric rate of 15¢ per kWh, it would cost 6¢ per hour on the low, 400 watt setting, and 12¢ per hour set at 800 watts.
Additional features appreciated by actual owners are its light weight portability, tip-over shut-off protection, and noise free operation. The reason it runs so quietly is that it doesn't have a fan. This is a big plus for most people, but disappointing to those looking for faster room heat up times afforded by a fan.