Good find Phoenix. Not only will it save a bit of money but it should prolong the useful life of the miners by making them slightly more energy efficient.
And add a bunch more financial overhead that you'll likely never recoup over the lifespan of your mine. You need to be serviced by a shitty power company that has poor service for a P.F. Capacitor make sense.
Not only that, but any savings are marginal at best. If you take the first row of the chart on that webage as an example, the proposed savings is ~1.23% assuming $0.12 kW/hr.
Also, it won't make your miners more efficient, all it makes the distribution network more "efficient". However, that's only if your supplier is billing you like a dick in the first place by billing for total consumption and not on just the active power consumed.