I have a Giro air attack shield. It is a bit hotter than my road helmet. However, it is subjective on how much heat you can tolerate and what kind of climate you live in. One thing I noticed about the shield version is that it actually ventilates my face a lot better than when I am wearing sunglasses. The shield sits away from my face and lets air circulate.

Regarding aero-ness. I use my air attack on the track, and when I am spinning with my head down at 38mph, I can hear the wind rushing over the helmet. It is a super cool sound.

I think it is pretty much established that aero road helmets make a difference. how much, and how much it means to you is a different story.

I think bell is about to release an aero helmet with close-able vents:
Gallery: New tech at the Tour of California - VeloNews.com