I just tested this case submerged in the sink with running water and paper towels inside. I shifted it around and the seal held. When I forcibly held it down with the weight of a coffee cup, air bubbles starting coming out of one of the clamps. I removed it and sure enough the towel was starting to dampen. However when I opened it, I saw that I had been careless and left part of the paper towel in the seal line. Dried it out and tried again. It stayed dry after an hour submerged.
However when I went to put the lanyard on, one of the plastic clamps flew off! I refastened it no problem, but after reading the review about the clamps loosening after just a couple uses, I'm still nervous. May do another test, before I'm comfortable to use with the phone enclosed. Will report back results.
** Update: used in the Carribbean while snorkeling on multiple trips for extended periods of time. Put a piece of paper towel in with the phone as my "early warning system." It worked flawlessly and took AMAZING photos. I even took great pictures through the plastic above the water. I'm a believer.