Gyro sights work extremely well for tracking shots where you have a steady tracking solution and an accurate range.
Disturbed reticle gunsights are not HUDs in definition. Alone, they provide no displays pertaining to the performance of the aircraft you are flying. A HUD generally provides some of the "head down" information obtained from the cockipt instrumentation and displays it to the pilot through the combiner glass. The early gyro sights (the US' K14b, for instance) were strictly mechanical and provided no means for displaying anything but the actual projected sight image.
MiG