I really like Specialized gear. They design really nice stuff at somewhat affordable prices. This is a well made vest. It keeps you warm and vents heat out back.
However, it flaps in the wind in the aero position. It gets very annoying and loud with the nylon flapping near your ear. When you’re down in the aero position trying to create a more slipstream position, say, during windy days, air gets in around the arm holes which causes the flapping. It’s properly sized because it fits tight but not race skin tight. I tried everything from pulling it down as it tends to ride up a little. I believe it all comes down to the lack of elastic in the arm holes. It just doesn’t hug your arm enough. In the aero position, I pinched my one arm hole tight and the noise went away.
If you’re a slim/med build, you may find this vest very irritating. I’m a 5’-6”/155lbs male w/ athletic build - aero road bike/slammed stem - size medium in everything, small would be too tight.