Thanks, everyone. I must have been incredibly unlucky when I looked!
I like the bags because I can fit more of them in the freezer than with bottles. Also, if you defrost the milk overnght, then I would just empty the milk into the bottles before I went to work each day - all lined up in the fridge, ready to go. OUr helper is 100% trustworthy, but I like to do it myself.
I also like the bags because I woud write on them when the milk was pumped. Pencil would come off the bottles, stickers get all yucky and indelible pen - well, you get it!