AoA is only useful when the wing is clean. If anyone wants information on the only device that will tell you the margin remaining to the stall on an iced up or otherwise contaminated wing, please send me a PM.
The Airfoil Performance Monitor works by measuring the ratio of turbulence to smooth airflow and gives remarkably consistent indications of how close to the stall you are regardless of the AoA when the wing is contaminated. Also works on the takeoff roll at a very low airspeed to tell you that your wing is contaminated.