Be careful here. This device will reduce energy consumption as claimed, but it also will reduce lumen output by about the same %. The Property Owner needs to be aware that his light fixtures will produce less lumen output (this is not a perpetual motion machine - think Ohm's Law - this is a simple give and take). If the area in question is overlit (not uncommon for existing installations 10 or more years old), then this might be a viable option. But be wary if the area is not overlit.
Another side-effect, color shift of lamps toward the blue-green spectrum. In the case of HPS, this could be considered a good thing and the mfr actually touts this as a plus on the web site. However, with MH this color shift may be to an undesirable Kelvin temp.
From what I can tell the device itself isn't smoke and mirrors, it simply reduces energy consumption and light levels and by reducing voltage. But the way it is being marketed is very much smoke and mirrors (mfr claims, "The unit reduces lumens yet increases illumination."). Like some others posted, I think there are some better alternatives for most applications. but in certain situations this might be a viable option, just be fully aware of what you are getting.