The Suspenz bag seems to be the best of both worlds. It feels more durable than the extremely thin bags, but is light weight. I have the smallest version and used it for my iphone, keys (with the electric fob) wallet and other 'essentials' for a 2 hour run. I tied it behind my seat where it definitely had the opportunity to get wet. It was a limited test - but everything was completely dry.
The bags also have a pretty neat feature of a clear (clear - but with a woven material through it -) strip down the bag from top to bottom so that you can see what is in the bag - I would imagine this would be most useful if you had several bags of the same size to know what was in them.
I am giving the bag a 9 due to limited use time - I will revisit this rating after the opportunity to it longer . Very good buy for the price!