Err... what for exactly? Inexperienced pilots are likely overwhelmed by everything they have to watch (I certainly was, especially during my IR training or when I started to train in the Pitts). And experienced pilots know how to fly the plane without one. Precisely the people who could in theory benefit from one (e.g. the guy who took his Bo into an apartment building in LA a couple of years back) almost certainly wouldn't be watching it or know how to interpret it anyway. If the stall warning (which is after all an AoA indicator, albeit somewhat binary) doesn't get your attention when you're in the conditions for an accelerated stall, you're almost certainly beyond hope.
Really the best thing to teach people is never to get into the situation where an AoA indicator would help them in the first place, i.e. slow flight. If I define "slow" as Vs1*1.4 (~75 KIAS in my 182), then even a 60 degree bank won't hurt you. You've no business to be flying that slow anyway except on final or on traffic duty. Anything slower is on the back of the power curve which is definitely a bad place to be.
Of course if people were taught spin recovery then it wouldn't matter anyway. But maybe that's a separate thread? You should be able to recover from a one-turn spin (i.e. enter, spin, recover) in 500' in any small plane. And, yes, I know, one-turn is really only an incipient spin taken a bit far, *real* spins start after three turns, but if you get that far then you're either very shortly to be dead, or you're doing it on purpose.
n5296s