It might be useful to show a student that the angle of attack for certain performance "speeds" was constant under conditions when the actual speed varied. But a trainer POH doesn't specify angles of attack corresponding to Va or best glide, so the student still has to learn to use the speeds.
I've seen two types of GA AoA indicators advertised, one with an external vane like on a 737 and one that measured the differential pressure between pinholes.
Here's one of the vane ones, complete with the manufacturer's arguments for its usefulness, and advantages over other designs:
http://www.riteangle.com/