Shawn, my reasoning is because megasquirt is simple. You have only a handful of maps you have to tune with Tunerstudio (IMHO the best tuning program out there for megasquirt). Timing, Fuel, Knock detection, Boost control, the main ones really. Having that lack of detail means it is easy to get in the ballpark and get your engine running pretty well. The fact that megasquirt can be set up to have an onboard ignitor makes it really convenient as well. However, AEM is a far more powerful system. With its plethora of maps, you can get more power out of the motor by being able get closer to the bleeding edge where the engine runs best, but is at its most likely to blow if something goes wrong. Megasquirt is also more user friendly than AEM is. I haven't messed with SAFC though.
Villy, I would love to, but it is kind of a custom-tailored install that you do with your car. We could do some sort of tech day install on a car sometime though. The best option would almost be to just send me the harness and I would remove the crap that you don't need anymore (like the ignitor and VSV's) and redo the harness so it was compatible with Megasquirt.