I have looked at the ebay link. These things do not do anything. That has been proven by Consumer Reports time and time again. Also reputable car show folks who have not been bought off by the manufacture of such a device also will tell you that those intake inserts are useless.
Don't waste your money on stuff which has no proven effect on vehicle efficiency or performance.
I do not wish to insult your dad, however, most of the time these types of vehicle "snake oil" items are very placebo in nature. You install them and then you convince yourself, self-consciously, that they were not a waste of money and are doing what they advertise.
I'm an old marketing major; I know, marketing is very powerful. It can convince people to buy stuff because it will make them look sexy or feel better, when in actuality the product will do nothing like that. The same goes for a lot of auto parts offerings.
If you have a Prius, just drive it like it is.