In comparing the EFIS offerings of GRT and AFS, they take different approaches to the design of their AOA systems. AFS measures differential pressure from the leading edge of the wing while GRT's output is derived from an algorithm. I'm attracted to GRT's system since it overcomes the need to measure air pressure where there's always the possibility of blockage from insects ice etc. Has there been any third party evaluation of these two systems? Does GRT make any trade-off in not requiring measured inputs of air pressure?