Caution: Rant ahead
Every residential power meter I've ever seen only charges for real power. Vars are not charged. So other than copper losses, I don't see how residential power factor correction could save any money at all.
Let's take a look at the copper losses. As I understand, this thing is installed in the main panel, so any inductive load copper losses from the panel out to the device are not mitigated. So the only piece left is the copper from the main panel to the meter - generally fat wire and short. Not much loss there.
Now for the case where the inductive device is off. Now the caps make the pf go leading, current is up. So what is being saved while the load is on is wasted while the load is off. Gee, sounds like the customer is as well off with the $aver as without it - well, not quite as well off, they have less money.
Save 25% on ones electric bill by getting rid of copper losses - That's a flat out lie. Save 1% on ones electrical bill - That's a lie.
Personal opinion: Any company selling them is part of the lie.
Okay getting off my soapbox - thank you for your time
carl