Depends. Most devices that came really works to bring your power factor closer to 1, say .9
With electrical motors, like the
fridge, specially and older one can have a PF (power factor) of anywhere between .5 to .8 and the electrical supply charges you extra for running such inefficient devices. How they calculate this extra charge is complicated, but for simplicity you can assume that you units will be increased by the difference in .9 and .8 (actual PF reported by your meter). So .1/.9 X your units is the extra that will be added.
Why these devices did not work for us is because in India the energy suppliers are still not charging residences based on PF, it is only for commercial and industrial meters.
Having said all of that, there may be some unbranded devices which are really a scam.