I had been using the medela bags as they are the same brand as my pump. As an exclusive pumper those bags were very expensive and not user friendly. These bags are able to lay flat to freeze which allows for better storage, also they are easy to pour into a bottle! Great quality for the price!!
I've tried a few other milk storage bags and this are by far my favorite. Although they don't attach with the stickers to the pump to express right into the bags, I found that it is much easier to express into a bottle and pour into the bags like these require. The bags that attach to the pump make spills a lot more likely! These are the only bags I will use.