I bought a harkila backpack earlier in the year. The Meikak, I think it was called. Nice Loden Cloth and not cheap. I used it once and it failed half way up the hill. I did n't have much of a load - just some lunch, water bottle and a fleece. A shoulder straps pulled away from where it was stiched in to the bag.
It was stitched with just one line of stitching - ie three stitches holding all the weight on one side. This was a 40 litres mountain pack and would expect it should be able to carry 15 to 20kg - ie a good load of meat etc. It failed with about 6 or 7 kg.
Thankfully I was carrying my rifle in my hand at the time rather than attaching it to the sack.
I would look very carefully at their construction - they look nice, but.