From what Jim@ERO sports has posted previously the order of "aero-ness"
(fast to slow)
1. Spec Evade,
2. LG course
3. Giro Air Attack.

All of these are aero helmets.

Not affiliated with LG...they're just a client like everyone else who pays us to test product for them. For that reason, the results are their's to share as they'd like, including what helmets they tested against. I can tell you they weren't afraid to test it against any manufacturers dedicated aero road helmet and the athletes we tested with that day were also measured with full-aero helmets, so there are numbers out there. We're also beginning to realize a particular manufacturer is quite confident in their products when they leave them for our athlete-clients to try during their personal fits and/or aero tests.
I think it's always safe to say an aero road helmet is typically somewhere in between a standard road helmet (whatever that means these days... the lines are blurring) and the newer dedicated aero helmets. Not as fast, but a clear time savings. Hopefully I won't get myself in trouble with this, but when Crowie tested the new Evade, it was very close to the TT02, which was quite surprising (not surprising to Specialized, though). I would say the Course is right there with it. Hopefully you're getting my drift. :-)

A few aero road helmets got tested. The consensus was you can do a triathlon in them but they are not faster than a real aero helmet. iirc we nicknamed one of the aero road helmets "The Salad Bowl" bc that was it's best use.
An interesting find was we did have one person who's regular road helmet tested out faster than their aero helmet. We found an aero helmet that worked extremely well, much better than the road aero helmet.

I think the what was proven is a real aero helmet is substantially faster than aero road helmet.

Per road bike action's wind tunnel test:
1. Evade (0.225 CdA), 2. Air attack (0.228), 3. Course (0.234).

Of note, Giro Aeon 0.234, Bell Gage 0.234, Prevail 0.235, so in other words, LG Course didn't seem any more aero than any other non aero, ventilated helmet. Maybe I'm misinterpreting the data, but a Giro Selector was 0.223, so I took it to mean that the difference between a full blown aero helmet and an air attack 0.005 was the same as the difference between the air attack and the Course 0.006, which is astounding.

That said, I have an air attack and a course, and like both. I can't tell any difference between the two in terms of race times or "feel" on the bike except for a temperature difference on my head due to the difference in ventilation.

Forgive me, but all I know about CdA is Lower=Better... What're the implications of 0.00X saved, in say Watts or seconds??

I used the Evade for the first time last weekend at the Mooloolaba Triathlon, my previous helmet was the selector. Rode a PB (57 low) to boot.

I am amazed how well this tested because the venting is really impressive, especially needed when it was humid and in the mid-30s.

The only thing I've found is that the helmet does fit a little differently than the prevail. It's a little tighter in the back of the helmet (that's just me). Whereas the prevail fits perfectly the evade is noticeably uncomfortable, but the Large is WAY too big me. It means this will only be used at races (which really isn't a huge deal as the amount of venting it has means it won't be much different to wearing a prevail on a really cold morning).