The Atmos would have been okay for me, but it seems Giro decided to leave out any pads on the top of the helmet. The postage stamp sized "excuse me" pad on the crown doesn't count. If the crown was smooth, it may not be an issue, but it's not.... so it digs into my skull in one place where the roc-loc attaches.
For reference, I use a Pneumo. I've also used the Ionos and Saros/Athlon, and even some of their lower-end helmets.... all of which have pads on the top of the helmet and feel great. It appears the Atmos is a bit of anomaly. Of the Giro's I've seen, the Atmos was the least well finished of them, meaning irregularities in the roc-loc attachment to the helmets, sloppy velcro attachments, and sharp points in the front of the Atmos. The technology may make it a high end helmet, but by the sloppy construction I'd think it was a $50 helmet.
The Ionos and Saros are both fine helmets. The Saros, which is noticeable more narrow in the width and outer profile than any of these helmets, is a nice new addition. I can't say I notice ventilation difference between any of these Giros despite the claims, as I am a human and not a test dummy.
To place a relative value on the Atmos, it's not worth it for myself. Everyone's different though, so try one.