I’ve got loads of them bought when they were on sale or to top up orders to get free postage, they’re made from a thin ripstop style material (my sleeping bag one is actually e-vent) much thinner than most drybags which are made from PU coated nylon usually.
Great for stuffing inside another bag to keep stuff dry/separate (sleeping bag, a dry set of camp clothes, down jacket, etc) in a non-waterproof frame bag, as they weigh a fraction of what normal drybags do. But I’d not use one strapped directly to the bars as it would probably wear through. Having said that I’ve never punctured one.
It’s not really comparable to alpkit/ortlieb/lomo/sumit2sea stuff which is probably tougher, but significantly heavier (my bar bag is an alpkit bag with separate podsacs inside for sleeping bag, clothes etc).