At first, I think I'd be worried about my center of gravity shifting around just as I was tackling tricky terrain.  Could be that this pack actually "reduces" that problem and I'm sure my brain would subconsciously "adjust" somehow eventually.  Nevertheless, I suspect the learning curve would be significant.  The older I get, the more I visit my orthopedist... and the more I deal with stability issues.  I REALLY don't wish to invite any more.  I'd need a significant trial run before buying one, for sure.

Any resident physicists care to comment about the effect on one's "center of gravity"?

Jimbo   8-)