with a pocket nappy, you have the shell, and the material that is against bubs skin, and then you stuff the absorbant materials in between these two layers. the outers dry relatively quickly, and you can have extra boosting so you can use the shell wash it, let it dry (some of mine dry within hours in the right conditions, and even if that boosting isn't dry, you can use another set. you can essentially use anything to boost, provided it fits in the pocket

with an AI2, the inners are generally tailored for the nappy, and like you mentioned, they snap in. we have added boosting to some of our nappies as DD has times that she is peeing like nothing else, but when you put the nappy on them, you have to make sure it's all laid in properly. much more painful to do. thankfully it's only been the Ittis we've had to boost more, everything else seems to have enough - so we just keep the Ittis to use at home.

with either system though, you have to make sure, if you've boosted extra, that you still get a good fit around the legs - if you don't ahve a good fit, you will end up with leakages no matter how much you've stuffed them with boosting