Long ago, I had countless ziplocs leak air, however slowly, and things get freezer burned in them. Also, I have not found any other plastic bag type that would not odors to permeate, either inside to the out, or visa-versa. How many of you have had some butter in a ziploc, gone to use it, and there was a taste besides butter? I keep it in glass jars, but that's because this happened, at least once! When I first bought a Foodsaver, I tested this by sealing some minced garlic in a bag, and even after it had fermented in the bag, the odor could not be smelled. Try that with a ziploc, or other bag.
I buy the "bags" in rolls, in large numbers, which is much cheaper.