The Gunrunner is a small day-pack with minimal shoulder straps and waist belt meant to allow great freedom of movement and the ability to shoot with the pack still on. It's not meant to carry much more than your rifle and 5-10 lbs of gear. All the weight is carried by the shoulder straps. The waist belt just holds the pack tight to your back.
It's a very popular little day-pack if that's what you're looking for.
I'm also curious about this little pack, I've got several big packs but this would round out the "backpack quiver" as the lightweight go to pack. I looked for youtube video gear testimonials but haven't found any yet.
I just finished a spot a stalk bear hunt in Idaho and I used the gunrunner as my daypack and to carry my rifle. It worked great leaving my hands free to use the walking stick.
I thought the waist belt carried some weight and my shoulders/back never got sore or hurt. I think from the way it worked for me I will use it a bunch.
The rifle I used comes in at a little over 8 pounds. I would guess the pack, rifle and gear in it were in the 15 to 20 pound range depending on gear for the day.
If you look over the attached link to Eberlestock's website, and watch the embedded video, the Eberlestock folks will show you the proper way to adjust the pack so the weight rides on your hip where it is supposed to ride. The mid range and upper end Eberlestock packs all have adjustable yokes for the shoulder straps to adjust for your torso length and removable hip belts. In addition if you are short, or tall, or thick thru the middle (like me !) Eberlestock also sells XL and Small shoulder yokes and hip belts.
The Gunrunner packs have the wider opening to allow larger rifles and optics. Good news, it is easy to put a very large weapon in the scabbard. Down side (versus packs with smaller scabbard openings) is that you have to really crank down the compression straps to keep a normal size rifle from "sloshing" around in the scabbard when you are walking quickly. I do not own a Gunrunner. However, I have no problem doing 3 mile training hikes with an 11 lb rifle and 40 pounds of ballast in a properly adjusted X1, X3, or J107 pack.
Properly adjusted, the Gunrunner will not be the limiting factor to your hunt.