I bought my Amigo Pro filter in 2007. While Brian Frankle switched to the Katadyn Hiker Pro filter that year, he kept the silnylon water bag with the configuration he'd had the year before (2006) (which did have the water filter inside the bag). IMHO, the one weakness was that it's extremely difficult to hold the water bag open while dipping water into it from shallow places where you can't dip the bag. I'd rather have a tailored water bag that could be held open under those circumstances.

My Amigo Pro water bag started leaking severely last summer. I haven't been able to find a hole, but it loses its contents in about an hour and it is difficult to keep the drips from contaminating the output. I was going to get a new one, but the ULA new management stopped carrying it. I'm therefore going to make my own bucket and use the existing Amigo Pro hardware (with a new Hiker Pro filter). I hadn't thought of cuben, but it sounds like a much better idea than silnylon!