In their public videos, Red 6 shows pilots wearing their AR helmet while flying in Red 6's own ultralite demonstration aircraft. There has yet to be any details on how they would integrate their system into an F-22 or F-35 helmet, which both have considerable AR capability built in.
One issue is that the bright AR target is superimposed over the darker environment. There is no way to show a dark aircraft against a brighter sky. It is also not clear to me how they precicely update the location and orientation of the training aircraft. It appears that their system works without an instrumented test range, which get's us down to onboard DGPS and maybe some fancy inertial stuff.
In adition to dogfighting, they have also demo'ed aerial refuling training with am AR image of a KC-46.
C++ is the best example of second-system effect since OS/360.