I have not flown the AFS unit, but have quite a few flight hours with the GRT, and have reviewed and commented on it here before. If you want a full-time indication of AOA, no matter if you are at th top of a loop, then a measured system is probably the way to go. If you are looking for AOA on approach, then the GRT system is quite adequate - because it is calculated, and requires computation, it is not perfect in highly dynamic situations, but gives good data within a limited set of operational parameters.
The biggest plus with the GRT AOA is that it is free with the EFIS, and requires no plumbing or installation. The biggest problem is that the display is on the EFIS, and generally out of the field of view when you are in maneuvering flight (because you're looking out the window). A remote reading head that mounts on the glareshield would be a great addition!
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)