why do you need carbon at all? it's not a neccesary item in most cases. fill the chambers with floss or something productive. that's all i ever do with my 404's. 2 chambers of biomax on top and then 2 chambers of floss on the bottom (for lack of something better to put in them).
just for the record tho, to answer your question. the "bagged" carbon is a fluval product. if you buy or open their little box of carbon you might see something that looks familiar. i think this is their idea of pre-measured doses to make it eaiser at filter cleaning time. another thing is, these bags will degrade eventually and when they do, yuck! i had this happen before, it makes a serious mess. in the x04 series the bag is pretty neccesary, the carbon is too fine to just go in there by itself. it will get thru the slots.... maybe the cheaper carbon wouldn't because of a larger particulate size tho.....
good luck