I have Syntace C2 aerobars on my bike. Where I'm from, the wind is always blowing, so they really help on those long upwind legs. The Syntace bars are adjustable for width, length is determined by three different sizes, and very lightweight. They DO block the top of the bar for placing your hands there, but the ability to ride the aerobars trumps that as a negative. I love'm!
Had the Profile bars with the spring arms, and both sides broke the springs in less than a year. Replaced in warranty, but still a hassle.