I also have the Kifaru gun bearer and it's awesome!
Here are some tips after using it for 3 years.
1. Use some sort of protectant or even duct tape between the GB strap and your waist belt. After a long season of hunting, the GB rubbed almost through the MR pintler waist belt. I think this was made worse because the Pintler has a plastic insert in the waist belt and it really rubbed on the edge of it. I ended up putting shoe-glue on the waist belt to give it some protection.
2. Play with the high of the strap to fit your pack and type of rifle/scope. I found that if it was too high, the scope would jam into my arm pit. If too low, it would hit my leg.
3. If you're rifle has a stainless barrel or shiny blue barrel, the head lamp will reflect off of the barrel when hiking in the dark. I ended up taping my barrel with some camo cover tape. Just something to look out for so you're not blinded the first time you turn your headlamp on.
4. The GB upper strap disconnect I was able to weave it into my MR Pintler chest strap clip. Worked great and it has stayed sturdy.