At speed the cooling is great, even in +25C I can feel the air flowing over my head. (Buzz cut)
In long climbing situasions in hot climate I would go with something with more vents.
I have the shield version for the track because it is the perfect omnium helmet. A bit more aero than road helmet, and (way) more ventilation than a Casco. Perfect compromise, right tool for the job. It seems like the perfect crit helmet as well. And while I agree that it would not be my choice for long climbing in hot weather, I was pleasantly surprised when I wore it during a track event in San Jose last month during a heat wave (high 90's), with no noticeable issues.
The shield is in my opinion a bigger advance than the aero thing, hope someone comes up with a magnetic visor for a vented helmet.
Agree that the shield version is the way to go. While I have yet to see some solid data, I suspect the shield will end up providing nearly as much of the aero benefit (if not more) as the lack of vents. Besides, it looks kind of like a mushroom cap without the shield and pretty badass with one.