Many groups ban aero bars, but as I've gotten faster and starting riding with faster groups, I've found that those groups are okay with them. I see quite a few of them in pacelines now, and don't have any issue with them. Just as "It's the motor", it's the skill of the rider that matters where safety is concerned. I'm more worried about me than I am about the guys I see with aero bars, who generally have far more experience than I do.