I have both name brand and inexpensive ones and really can't tell the difference. Once I needed to take 3 quilts to New Mexico and put them into 2 bags - 2 in one and 1 plus sweater in another. They really saved space in my suitcase.
I also have several small ones that you can roll up to squeeze air out of them and don't need to use a vacuum. These are great for my little travel pillow and some other things I carry on the plane. It makes them all fit neatly in my carry- on bag. One trip it really impressed the man sitting next to me who thought it was a neat trick.