If you're in the market for a 24-25 liter backpack with a suspended, ventilated mesh back, you'll probably come down to this brand new model from Deuter, the Lowe Alpine Airzone 25, and the brand new Gregory Z 25. I'm sure Osprey has something too, but Osprey is not my personal preference.
I have a Deuter AC Lite 18 which is a fantastic little daypack. I use it all the time, however 18 liter is sometimes too small, especially if you need to carry multiple layers. A 30 liter is in my opinion a bit too much for most day hikes, so the 25 liter packs neatly fills in this niche.
Given my great experience with Deuter I had big hopes for the new AC Aera, and make no mistake, this is a great pack. Its main, unique feature is the bottom zipper that lets you access the contents at the bottom of your pack without having to empty everything from the top.
But, I decided to return the Deuter in favor of the (also quite new) Lowe Alpine Airzone 25. Because of this I have not actually used the AC Aera, so this review is based on me comparing the two at home.
The AC Aera is almost a pound heavier than the Airzone. And, if you compare it to the Gregory Z 25 it's almost two pounds heavier. Comparatively then, the Deuter is quite heavy.
The back mesh design on the Deuter is one large, continuous mesh, while on the Airzone it's actually more like two strips of mesh, which should make the Airzone even more breathable. That being said, and this is something that is not easy to tell from the pictures, the AC Area has a much larger curvature of the opening in the back. It also goes all the way down to the very bottom of the pack which makes it ventilate even around the hip area. The Airzone has a smaller curvature and the hip area does not have an open space behind it for airflow. However, due to the large curvature of the AC Area, the storage compartment is quite noticeable curved as well, while on the Airzone it's much more straight down. This makes the Airzone easier to pack.