Snake oil!
Although maybe in combination with a
power conditioner, a
hyper voltage system, and a
Tornado you could get like 75MPG and another 100HP!
In all reality if a vehicle ends up benefiting from an upgraded grounding system it's purely the result of the original one either being insufficient (whether from the factory or due to end user upgrades) or defective. I had a vehicle where the primary grounds from the battery were corroded inside the wiring badly. Fuel economy nor power seemed affected, but things like dim headlights, a weird sounding horn, and an inconsistent idle did happen.