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I've noticed the air fences on the front of trucks for a while, but was unsure as to whether they where aerodynamic or sacrificial plastic in case of bumps and scrapes.
Regarding fences in general I think in the vast majority of cases they are a waste of time, certainly when you are not actually using the air for anything and simply trying to maintain a clean flow.
Winglets on plane wings are functional but take 100s if not 1000s of hours in wind tunnels to perfect as they are very specific to each wing design. Earlier "bolt on" designs were of limited benefit economically as the added weight and cost actually gave little economical benefit over fuel savings but did allow airliners to appear more modern. Winglets that are integrated into new design (787 and A380) are far more effective from what I've been told in my studies.
Multiple fences on flat surface are simply increasing frontal area and can possibly cause more turbulence that they prevent. Don't forget you are creating further edges which will lead to further issues at the edge were the two separate air flows meet again.
And then finally there's the side profile, greatly increased but for what real gain?
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