I've had a size medium for a few years. The zippers strike me as medium quality - but I don't use them much. The main compartment of the bag isn't zippered, the top just folds over and sticks with velcro and 2 plastic snap-buckles. So it's somewhat insecure in that respect - if you turn it upside down and shake it things might fall out. That doesn't bother me that much, but TBH I think I would prefer a zipped up main compartment.
Overall I really like the bag and use it a lot. No sign of defects or poor design, other than you can't turn it upside down and shake it. I think the strap system is great, with the 2nd cross strap you can strap it tight to your back and run or bike.
FWIW:
http://www.bikeforums.net/general-cy...rando-bag.html