I checked the web page in the OP. There wasn’t much technical info there, even under the specifications section, so that makes it difficult to say for certain whether the device in the OP is a worthless piece of junk or not.
Residential power factor correction devices are completely worthless. Power is made up of watts and vars. Most folks have heard of watts, but not vars (var = volt-amp reactive). Watts are the power that is actually used, like for example the electricity in a light bulb that goes into making light and heat. Vars are a bit harder to explain, but if you have a simple coil of wire (an inductor), if you run current through it, a magnetic field develops which stores energy. Remove the electricity, and the magnetic field collapses, releasing the stored energy in the form of electricity again. Since residential power is an alternating sine wave (hence alternating current, or AC) any inductors will be constantly charging and discharging. The energy isn’t doing anything useful. It’s just being temporarily stored and released. However, it does take current to charge up the device, and hence some “power” is used to charge the inductors, even though this energy is later released.
Capacitors do the same thing. A really simple capacitor is just two metal plates placed close to each other. Instead of storing energy in a magnetic field like an inductor does, a capacitor stores energy in an electric field, but it’s the same basic idea. Energy is stored and then released later in the AC cycle.
Inductors and capacitors are “reactors”, which is where vars (volt-amps reactive) comes from. In an AC system, inductors and capacitors work kinda opposite of each other, since while one is charging the other is discharging, and vice-versa.
Most residential loads tend to be slightly inductive, due to things like motors in your refrigerator, washing machine, dryer, vacuum cleaner, hair dryer, etc. You can balance these out by adding capacitance to the line, which is what these power factor correction devices claim to do (but don’t, which I’ll explain in a moment). Power to your home is most efficient when you get capacitors to perfectly balance out the inductors. That way, the capacitors supply power to charge the inductors during part of the AC cycle, and the inductors supply power to the capacitors later in the AC cycle. The reactive power just ends up bounding back and forth between the inductors and capacitors, and the power company only has to supply the real power (the watts). When everything is perfectly balanced like this, it is said to have a power factor of 1 (or unity). If it is not balanced, the power factor will either be leading or lagging, depending on whether the load is more capacitive or inductive.
This all sounds good in theory, but the problem is that the devices sold for home use are just capacitors in a box. They don’t monitor the power factor at all, and aren’t switched on and off of the line as needed. Instead, they constantly adjust the reactance of the house load whether it needs adjustment or not. This is why they don’t work. And, they can’t possibly save you money because all they affect are the vars, which you aren’t charged for anyway. The old fashioned spinny wheel type power meter only measures watts, so the power company can’t even tell how many vars you are using even if they wanted to (unless they hook some measuring equipment up to your line). The newer digital meters can measure vars, but even then you aren’t charged for them. If your power factor is far enough out of whack the power company may pay you a visit and tell you to fix it, but it would be very difficult using standard residential type stuff to get your power factor that far out of whack. Let’s face it, not very many people have 1,000 hp motors running in their basement.
If you are a business owner, though, things are different, and it’s important to note that the unit in the OP was installed in a business. Business and manufacturing customers have different types of meters installed, and these do measure power factor, and the power company charges them for the vars. In fact, the power company often charges them out the wazoo for vars, giving them a really good incentive to hook a power factor correction device up to their heavily inductive loads. A proper power factor correction device will monitor the line and will switch capacitors on the line as needed, or if you have a big machine that is very inductive it may have a power factor capacitor added to it which is switched onto the line whenever that specific machine is turned on.
It’s not clear from the web site in the OP if their device switches or not, so it may be just as useless as your typical residential unswitched capacitor boxes, which are just a waste of money.
Most businesses that need power factor correction also get three phase service, but that’s not strictly required for power factor correction to be important.
Power factor correction is generally done at the substation. I’m sure there are older systems out there that just assume a constant power factor and correct for that, but it is my impression that most of the power companies these days monitor the lines and switch the capacitors on and off the line as needed.