I only use Aerobars for my Time Trials. They definitely help me to stay down which creates the smallest position for me to punch a hole in the air. I use the Profile Design Wing model-arm rests are spring loaded and are raised off the handlebars when not being used. I wanted to get a Syntace model but they did not make one that would fit my larger 31.8mm handlebars.

I agree that it's nice to have the option to move into other positions on rides. I could use mine on solo rides but those are becoming less frequent these days. I certainly don't need the extra weight for some of the climbs I do. I also would not use them in group rides as I need my hands closer to the brakes and shifters.