Real science behind them...
Aerodynamics Research Revolutionizes Truck Design
Like any aeromod, you need a special case to see a big effect. Eddie's video shows a special case. Incremental beneficial aero effects are small, with large downsides when done poorly. On most modern cars, the latter generally dominates as factories have wind tunnels and real engineers; if VGs were aero-salvation, they'd be on the cars now.
Have fun,
Frank