- Familiarity: I've put it through the wringer
Just returned from a backpacking trip around Europe with this as my only bag. The detachable day pack is wonderful and I found it very useful. I wouldn't recommend keeping anything inside it when it's attached to the main bag because it makes it difficult to attach (I initially viewed the day pack as an extra storage space, but it loses over half its space when it's [slightly] folded and zipped to the main pack).
As for the main pack - entirely too heavy. I understand the support system adds some weight, but I didn't have a lot packed and it was literally weighing me down. As an example, during my laundry day, I shoved the majority of my clothes into the day pack. Remaining in the main pack was only one day worth of (light) clothing, my toiletry bag (mini bottles of everything and an electric razor), a sleeping bag and a pair of light sandals. The day pack was light as a feather (even packed full with all the dirty clothes). The main pack was still heavy.
It was overly bulky for the amount I could carry inside it. This made it very difficult when jumping onto a cramped subway or fitting it into a storage compartment on the train.
I served in the military years ago and was given a basic, standard issue MOLLE ruck sack. I would have traded this Deuter on the spot to have that ruck sack back.