I love the Zeitgeist (I've sort of gone a little nuts with them - up to four now), but I think this one is my favorite! It's the Taiga/Coyote one, which is a gorgeous color. I think it's become my fave TB colorway, as well. This bag is super light and these are the most comfy small backpacks that I've ever found!
I tested this one out today for a little light hiking at Phinizy Swamp, Augusta, GA (yes, I know, it doesn't have the proper back panel for that, but it's small and light and it was a short hike of about 5-6 miles with a few stops in mild weather in an area with good cell service). I've removed the sternum strap on all four of the bags because the shoulder straps fit solid as a rock, and it's almost like I'm not carrying anything, which is very nice.
It will fit my Black Halcyon SE (packed out as my EDC and in the main compartment vertically), protein bars, an 18oz. wide mouth HydroFlask (vertical next to the SE), Packtowl Nano in a pouch, chap stick, sunscreen stick, cough drops, tissues, hand sanitizer, half-Buff headband, small first-aid kit, a map, keys, and a packable sun hat with no issue! I could have fit a light rain shell or long sleeved tee tucked into the top of the bag, but the weather was so nice today that I didn't need one.
Love love love love love!!! ❤