Magic Link is pretty worthless. Monitoring the power consumption of an iPhone after charging, it takes more than 2 weeks to register even 0.01Kwh. You'd have to leave your phone plugged in for years and years to recoup the cost of that cable.
When a phone isn't plugged into your standard Apple charger, it consumes nothing. At least nothing registered after 2 months of leaving one plugged into a Kill-A-Watt meaning if it is using power, you're talking about less than 0.00Kwh in 2 months.