Here's my thoughts on the x-1 eberlestock
If you look at a side profile of a person the middle of your back and your butt stick out.
The inward curvature of your lower back gets spanned/bridged over b/c the rifle is pulled against the middle of your back and against your butt.
So the pack does not ride close enough to the your body -the more you put in it the more it pulls you over backwards.
Mine is good for pred calling and overnighters but if you start loading it up the rifle stays in hand.
I'm going to get a kifaru gunbearer and try it.