NASA tested the basic shape that is used by Airtab®.  They found them to be
the lowest drag vortex generator they had seen.  There are several technical
papers written on vortex generators and other drag reducing devices, (NASA Recognition Paper) and the Airtab® shape was amongst those tested.  This is not to imply that NASA endorses Airtabs™ - they never endorse commercial products.  NASA is using them in the Langley Wind Tunnel to improve the aerodynamics on standards and walls.

See: Picture of Helicopter in the Langley Wind Tunnel