My wife has a PK-AS on a goosneck mount on her AR-15.
Advantages:
Nice clear optics with minimum distortion.
Very long eye relief.
Black reticle, ability to turn on LED if you need it.
All zeroing adjustments are in the mount.
Range dial calibrated in MOA, so it doesn't matter what caliber you shoot.
It's made for Russian solders, robust, rugged, simple.
Disadvantages:
It's tall, no cowitnessing on this puppy.
Needs tool (3.5mm hex key) for zero adjust.
Expensive.
Oops, I was talking about this sight http://www.freedomoptics.com/comersus/store/comersus_viewItem.asp?idProduct=153
My bad. BSW