I want to know about this Power Electricity Energy Saver-Save 5 to 30%?

I just want to know about this thing call Power Electricity Energy Saver-Save 5 to 30% is this really work. Or if just a joke. I sow this device on ebay and wander is really work. They said you just plug it in and save electric by stabilizing the electric. Dose anyone heard of this thing it work and it legal