Very high efficiency, a cell the size of a dime makes about 40w of power in direct sunlight. No water needed, and way less land than bigger, less efficient panels.
http://emcore.com/solar_photovoltaics/terrestrial_concentrator_photovoltaic_arrays
Ben, every tech Ive found is worse, yes the less efficient panels are cheaper but you have to buy more land. Plus the bigger something left outside is, the better chance of damage by hail, wind, etc.
As to the size difference, you dont compare the cell size to the panel size of the competition, you compare overall size. With the panels included for both, the CPV structure is far smaller. Massive low efficiency solar plants arent an option because land is expensive near cities where the power is needed.
