I ditched the aero helmet years ago. Couldn't tell you time wise what you give up in aerodynamics, but I count the benefits of "no-aero" in different measurements. I use the Giro Synthe--a really light, semi-aero helmet that is one of the best cooling in the Giro line up. I overheat easier than the average person (read as "low thermostat')...plus, the advantage of less neck fatigue over any distance--which is noticeable even at 50-100 grams. Good bike position and keeping the head down will often negate what you see happen with many athletes.

They will keep popping their heads up every 10 pedal strokes and if a tailed helmet, put that big point up in the air and effectively "brake" and negate the aero helmet's advantage. Not to mention, I've seen so many riding the Ironman Course locally this past week, with their pointy little helmets sitting on their head so that even with their head down, still...the point is just sticking up slowing them down. This is common especially in the lower % of finishers. They have the "stuff" to look cool but don't use it right.

I go for cool & light with a bit of aero vs full on aero & it's made my racing so much more comfortable. As shapes and materials develop, I may go back aero as that gap slowly closes. But the comfort has been missing thus far from the lineups. Finally, you don't want to dehydrate yourself before the run begins from a hot helmet--if you're a heavy sweater like me. It'll help your run at the end of the day if that is the case, as keeping up with fluids can be an issue.