Well, they do. But, not for clothes. For big, bulky items such as my king size comforter, it worked like a charm. Shrunk that thing down to less than half it's size, and its stayed that way for days.
BEFORE AND AFTER
However, if you are good at packing up clothes, they are pretty much worthless. I don't see any reduction of space, and instead, all my baby clothes I packed up and tried it on are now all smooshed together in this super stiff plastic bag that cannot bend that takes up pretty much the exact same amount of space.
So, yes for big things, no for clothes. I may get a few more bags and pack up some pillows I have as well.