No it's not real., it's just a con. Such devices supposedly correct the power factor, but you're not charged for that anyway on domestic metering. Also modern LCD TV's have internal power factor correction anyway.
I have done power factor correction using capacitors because they made enough difference to change the size of the wires and circuit breaker on some big horsepower air conditioners. There is a purpose, but it is not about changing the $$$ on your electric bill.
Power factor correction (capacitors) can reduce the portion of the current which is not used as power by an industrial load of OLDER motors. A residential customer CANNOT use power factor correction save on his electric bill for several reasons:
1) Most of our load is near unity (lamps, modern appliances.)
2) Any others have a varying or unspecified power factor and we have no way of measuring it.
3) Most of our non-optimal power factor, if any, (Old PCs and entertainment eqp't.) is harmonic and cannot be fixed with a simple capacitor.
4) POWER FACTOR IS NOT CHARGED TO RESIDENTIAL CUSTOMERS.