from the picture it looks quite good.
the straps with rivets(horizontal) are designed to hold webbing pouches like water bottles or spare ammo pouches.
you will see the same design on "us alice packs" but theres no reason why you coulden't use it to strap on gear such as sleeping mats, tarps, axe ect.
the shoulder straps appear that they would put the pack quite high on the back probably so it sits above webbing. some people find this uncomfortable but it means you can wear a bum bag or simular.
one quite important point:
40l for one bag can be more or less than another it depends how they've measured it! some companies just measure the main compartment others measure every pocket! i don't know how the military do it!
with army stuff you can usually say:
it is made of tough material
therefore it will last a long time but will be heavy!
the flip side is that:
it possibly is made cheeply,
and the army dosn't go in for comfort for the individual!
basically what i am saying is go find one, have a good look at it try it on, if possible with weight in it.
my first impressions are:
looks like a pretty strong and usefull bag but i would want to try it on!