Firstly, I've yet to brew a thing, but I bet I've read more books and net material than anyone in my position. On another forum that is American based (perhaps brewer's round table, I've forgotten) there is a pictorial step by step guide by a young guy with long hair. He says he was getting great results and loved it and was coming from traditional all grain. It looked really easy, other than that bag of grain is very heavy after mashing (I think that's the term. You pull it up and let it drain out before the boil. I may have my terms confused.) Since he was doing it in the kitchen he didn't have a hook, but that would make it easier. My LHBS is now carrying these bags pre-made and when I get some extracts under my belt I'm going to try. I specifically bought a 7 1/2 gal pot so I can move up. It is possible according to him to do a partial batch and add water after to top off the fermenter just like an extract partial boil, but of course it wouldn't be the best way to go. I'll see if I can find it and come back with the link.
Bill