[MetroMPG]

Welcome to the forum.

I'll chime in on the skirt question: the smoother the better. You want them to stick out as little as possible. Also worth noting that the tire/wheel arch gap is already really good (small) on the Prius. Because of that, skirts may only be marginally more effective than going with full wheel covers.

Not trying to discourage your friend, but just keep things in perspective (don't be disappointed if he doesn't detect a giant improvement at the pump).