Aero tt helmets

I am not sure if this has been asked yet. I was wondering how many of you use aero helmets on training rides and on your tri's? Are there any real benefits to these helmets? I just wear a regular helmet. I keep hearing through all the searching I am doing that you save secounds to even minutes by wearing one of these. Also hear that some aero helmets are better than others such as helmets with covered ears and longer shapes fair better than shorter tear drop shapes with no ear covers.

Is there any testing done or truth to the aero helmets working, I am interested in getting one. But have not decided on which one. To those of you that ride with them, what brands are they and how do you like them. Just trying to get some feedback from everyone that has experienced a change in their times by wearing one of these.

Andy