Some basic facts:
Power factor correction is most cost effective when applied directly to the offending load(s).
Application at the service entry/panel benefits the utility but you will still have the same losses in your wiring.
Capacitive correction can make PF worse on loads already containing filter capacitors and rectifiers.
Subtle changes like reversing plugs and moving loads from one branch circuit to another can greatly affect PF of both branches.
Is it worth the trouble to correct it?:
Severe PF problems can shorten the life of equipment and appliances.
Severe PF problems often indicate equipment malfunction or impending failure.
Utilities are not allowed (in most cases) to bill for unused (reactive) power but it can significantly affect demand costs.
Inexpensive, passive methods like moving plugs, etc. are, indeed cost effective.
Losses such as frozen perishable goods due to load failure may justify cost.
How can mM help?:
Real time display shows PF conditions on each branch circuit and algebraic total instantaneously.
Making and keeping track of changes (passive methods above) can help you fine tune your total PF for better savings.
Small, inexpensive motor capacitors can be added to specific inductive loads if they are needed.
Small inductors (unused wall-warts) can be added to specific capacitive loads if they are needed.
Other devices and improvements can be immediately verified regarding their effectiveness.
Power Factor Correction Scams:
While there may be exceptions, a single correction device at the service entrance is unlikely to show cost-effective savings.
While there may be exceptions, a device plugged in to an arbitrrary receptacle is unlikely to show cost-effective savings.
Theoretical justification does exist but the savings or return on investment is often exaggerated.