I like the idea of secured cards for teens. The idea of AUs though to me is along the lines of teaching kids biking (good) also on the pedestrian crosswalks (bad).
The teen will feel good about a secured card, as in It's mine and I have earned it. The AU translates into Well, I'm really just an add-on, and I certainly don't feel like being monitored.
In a recent article about teenagers texting and driving, it was common that they don't listen to adults, but they do listen to their fellow teenagers. I say let's give them credit where credit is due!