I’ve noticed that every product I’ve bought in the past year with a zip-lock seal is destroyed with common use. I actually think the zip-lock itself has gotten stronger. The bag rips before the seal opens on half the bags now and whenever I try to opens bags I had no issues with before, I find myself stretching/warping the plastic before the seal eventually opens.
It’s pretty frustrating and I am seeing it across many products. Cheese bags, storage bags, snacks etc…
It works pretty well. You’re applying opposite sideways forces to the zipper itself rather than pulling on the plastic film of the bag.
Edit: if you want to be sure you don’t blow out the corner of the bag, pinch it with your other hand before sliding your thumb towards it