I recently ordered and lined up a Helinox Zero, Zero Highback, Big Agnes Sky UL and Helinox Sunset.
If you’re looking for back support the Highback or Sunset is going to be better. The Sunset is also significantly higher off the ground and heavier than the rest.
They all have slightly different positioning and a couple people all did a comparison when I had them setup here. Not everyone had the same opinion on each chair.
I really liked the Highback for sitting upright, but it is notably more of an upright position compared to the Zero and Sky UL and you can’t lean too far back.
I’ll be keeping the standard Zero as a super lightweight chair as it’s lighter and a little more versatile then the Highback for backpacking and maybe it’ll find its way on some bear hunt. I can lounge back a little easier in this compared to the others, but it’s not as supportive in an upright position. The weight is the lightest of all.
I’ll also be keeping the Sky UL. It’s heavier but also taller off the ground than the Zero and I used it when sitting for some whitetail hunts this fall. It’s a bigger chair as well for more layers to fit in the super cold days. I think the the Zero is a little too low for when the snow falls here.
The Sunset was even higher but I don’t see myself packing around a 3lbs+ chair when the Sky UL is almost as good for quite a bit lighter weight (not nearly the same back support though).
I found all chairs quite comfortable though.