I think most people that use them talk mostly of the dust and cleaner air benefit rather than the wading depth. Tbh, if you are planning on going into water deeper than the 700mm you get from the factory, then there are so many other factors at play. Diff breathers, water ingress to the cabin, grease in bearings, not to mention the danger of being swept away in a current if it's a river. If anything it encourages people with little experience to go into water they shouldn't thinking that the snork will protect them.
I don't have one, and won't. I've been through 2 feet of water a few times, but wouldn't like to go much more than that