I purchased the Zerk 40 when it was first introduced a few years ago on Indiegogo. Co-designed with The Real Hiking Viking, a renowned thru-hiker with thousands of hiking miles under his belt, it offers 40 L of lightweight load carriage.
Overall, the 2021 version is functionally the same. The biggest change from that first model is new materials. They’ve switched to 210D Extrema nylon and 100D nylon x span 840D stretch mesh.
It features a roll-top closure with SR buckles for security with a single strap over the top to help control the load. That strap is also long enough to stow a bear canister. Inside, a removable laser cut frame sheet (EVA Atilon) allows for rigidity and airflow.
The outside features five mesh pockets, dual pockets on either side for water bottles or snacks, and a large rear pocket. Bag size adjustments can be made at either side via a diagonal strapping system as well as via the bungee cord at the rear.
The harness is very comfortable with wide padded straps which almost form a vest front. There are two mesh pockets on either strap as well as a sternum strap with integrated whistle. The removable waist strap is just that, a strap, rather than a full hip belt normally found in packs, but the pack is intended for lightweight through hiking.
You can see the full features here:
I have configured the Zerk 40 as my “get home” bag and it accompanied me on every road trip. The colors are subdued enough to not stick out but also not look like a walking surplus store.
mountainsmith.com/products/2021-zerk-40-backpack