Do not be surprised if it does not work as expected. Most of these things are simply a power factor correction capacitor that is tied across the mains. While it may correct a lagging power factor (inductive load) and thus reduce current, it decreases the power factor when the load is resistive and increases the current. Some of these devices are so deceptive that they even install dummy components that make it appear complicated. Power factor correction capacitors do not alter energy consumption other than possibly reducing line loss in corrected inductive loads (much less than 1% improvement). This paper provides a good overview and explanation:
There is another type of scam device that is called a spike buster that claims to reduce power consumption by limiting line voltage transients. It would have some merit, if the power source was actually as dirty as they indicate, but this is not the real world. Understand that voltage transient protection is really a different issue that should not be confused with the spike buster energy saver.
On the other hand, I am familiar with the energy saver from the 1970s by Frank Nola that actively adjusts the power factor of an AC motor by reducing excitation voltage. It can actually bring marginal savings in lightly loaded induction motor applications, but such savings may never pay for the device--better to put the money in the bank--keep the principal and collect interest. It uses a triac to reduce voltage via the phase control technique. While motor excitation voltage is decreased that tends to increase efficiency, harmonics are introduced that tend to decrease efficiency, so the effect is marginal at best. Here is a modern patent that never should have been granted as it is obvious to anyone skilled in the art: It has nice schematic diagrams.