As I’ve posted elsewhere, I’m a fan of the Aarn bodypack concept. I feel more balanced, my walking posture is more natural, I have eliminated shoulder and back pain, and I feel less fatigued at the end of a long day.
I can’t account for Roger’s problems except to say that fitting is non-trivial and it takes some time to get the packs dialled in – there are far more adjustments than you have with a conventional pack.
I don’t get a warm chest – the front pockets have a bendable strut and airflow is excellent. I’ve worn the pack on long alpine climbs in roasting weather with no issues.. Most women seem to be fine once they find the right adjustments. My arms are not restricted by the pockets, though it took a couple of days to get this right. I can see my feet perfectly fine. Getting it on and off is a non-issue once you get the knack. And if the pockets were ever a problem, such as for a day with a lot of scrambling, I carry a pack large enough to simply put them in the backpack. Careful research by a leading ergonomics lab has shown that once you are carrying a non-trivial weight the additional weight of the pockets is more than compensated by the additional ergonomic efficiency.
Not everyone likes the Aarn, but it’s the most innovative pack out there and offers unique benefits if you do like it. Aarn has a happy band of enthusiastic customers.
My only reservation is the complexity and the weight – from the lightweight perspective they seem over-engineered. I have a prototype of a simpler design that offers pretty much the same benefits at half the weight.