My parents have had one for over 20 yrs. (actually on the second one now.)
It requires no electric and the unit itself does not require a filter. They did install a filter before the unit to help filter out iron and sediment. When the unit is installed there is a gear (on the original unit any how) on top that meters the water (based on water quality) once the predetermined amount of water passes through the unit, it switches from one side of the unit to the other. At that point it starts a backwash on the side it was originally on. There is little to no noticable loss of water pressure.
They do work. The company is based in Newbury, OH. (I have no connection with the company, just what I remember about the unit when it was originally installed.
Kurt