Easy to put on, good fit and comfort, easy to fit with the dial on the top of the helmet, and fits well with sunglasses. The obvious, and well advertised, pro to wearing an aero helmet is the aerodynamic advantage of the helmet.
None at the moment.
I tested the Giro Advantage 2 last year for a triathlon and a couple of time trials. It was the first aero helmet I had ever worn and I really liked it. That being said, I think I like the Lazer helmet more than Giro. The Lazer feels like it fits better and it has more venting. The Lazer has a nice and easy to use adjustment wheel on the top of the helmet that allowed me to get the correct size for my head almost instantly. There is a hole at the top that is used to poor water into, to help with cooling. I have not used the hole yet and it appears kind of gimmicky. I have a shaved head and my concern is that if I pour water in the hole, and my head is covered with sweat, all it will do is run it down my face and into my eyes, while I am biking. The prospect of that is not appealing.
There has been plenty written about the advantages of aero helmets and I am going to assume that since this is an aero helmet, I am getting an advantage from it. I purchased this helmet and I am very happy with the purchase.