The positives:
it has an excellent back fit for me. It really is very robust, you don't worry about damaging it. The gear loops on the waist band are very useful. The single strap closure is absolutely spot on.
The negatives:
Not sure it's worth the cost, even if it is bombproof. The cord grip closure that allows access to the main section of the bag failed first time out, so I've just replaced it with a cord grip from elsewhere. The elasticated chest strap has worn very quickly. The waistband closure straps keep loosening and require regular adjustment. The metal butterfly ice axe attachment points are too big to go through the head of my Grivel ice axes, so I've added extra accessory cord loops to them to make them useable. The bag would be perfect if it wasn't for these minor issues.