I received these bags initially from a milk bank when I had excess and loved them so much I continued to buy them when I found them online. These come pre-sterilized with the entire top of the bag sealed with a perforated edge. The Lansinoh bags also have a perforated edge for this as well. I prefer these over the other bags because the quality is better, the value is better, and I have never experienced leaks with these. Apparently I’m not the only one who thinks these bags are great because these have a 4.4 out of 5 star rating.
I used Lansinoh storage bags and pumped every bit of extra milk I had-- at five months old my daughter had an emergency open-heart surgery... she wasn't able to nurse or eat anything by mouth... the hospital let me bring these bags of milk in to keep her nourished and they were imperative for her immune system- they all fit in the tiny hospital freezer because they were frozen flat and stacked!
I have a Medella pump but I always buy these bags. The plastic is thinner which makes for faster warming. The Medella bags are stiff and not as easy to maneuver. The plastic is very thick and the seal is kind of tricky to get closed properly. However, the double seal on the Lansinoh bag is very secure and super easy to close properly. I lay them flat on a paper towel in the freezer then once frozen I stand them up in a long tupperware. Grandma watches our kids while we work so she is able to thumb through the stash and find the right amount. I always store bags of the current amount baby is taking plus 1 oz, 1.5 oz and 2 oz bags. We call them "oops bags" just in case someone spills when preparing the bottle. These smaller amounts also help when baby increases.