As with anything they're more how resistant rather than water or dust proof. My eberlestock did well at both. Recently got an AGC with the bungee closure but am not sure how well the lid will seal up while moving through the brush. The eberlestock closes up very tight.
AGC is what I have. I have not had any issues with dust or debris getting in.
As for rain I haven't had much experience with. I have only had it in light rain but nothing all day and soaking. In the light showers it is fine but if it was all day rain you would need to keep it covered. I believe it would eventually soak through.
I have a kuiu,fhf and now an agc. Agc offers the most protection and kuiu the least ime.
For some reason the kuiu seems to collect a lot of debris in the bottom of the pouch.
I have the AGC and while I have not had any issues with debris getting in it, it is definitely not waterproof and will wet out in a good rain. I sprayed my old ACG with Camp Dry after having it get soaked on my last hunt. I haven't had it out in any rain since, but I did run water over it and it seems to bead up and run off without soaking in. I also had Jimmy Tarps make me a silnylon cover for it and it fits very well but I haven't had the opportunity to test it out in a good rain yet. I just saw on Ebay that Jimmy Tarps is making them out of the green cuben fiber now and selling for $30.