I have one.
100% waterproof? Not sure. Water resistant? Definitely.
One caveat, if you want to protect your things from water, do not use the front pocket. the flap isn't wide enough, so it leaves some small openings on both sides. That was kind of a dumb oversight on their part.
Otherwise, great bag. Rode with it under some torrential rain a while ago and everything in it (main compartment, and "stash pocket") remained safe and dry til the end.