Speaking off the top, AoA indicators are simply the best thing to have among attitude measuring instruments. They are better than stall horns in terms of telling the pilot where the aircraft is in it's range of flight attitudes. They make the pilot who knows how to use them more aware of the energy state of the aircraft as attack angles change. Military aircraft have had them for years as well as civilian jets, because those aircraft operate at specific AoAs for best economy and maneuverability, among other things and the pilot needs precise info on AoA to do that. AoA data is used for many advanced flight management computers and is more often available in jets than in piston aircraft. The trend lately has been towards light-jet style avionics in piston aircraft, such as the Garmin suites we have now running digital AHRS units with digital autopilots, TAWS, and complex flight computers. Those systems need AoA inputs to function properly. Another factor in the adoption of AoA for GA lately is simply the lower cost of off the shelf AoA units plus FAA willingness to approve them.
I think it's a good thing for GA because stall spin accidents as well as overall student awareness is tied to seeing how things work. AoA gauges really show what is going on when you approach a stall, do a spin, or change configuration on approach to name a few common uses.