We have a lot of the travel Space Bags and we use them for every trip. With them, we can fit about a week's worth of clothes for my DD6, DH and myself in our larger suitcase. However, since we *know* we'll be buying souvenirs, and we'll need a couple pairs of shoes (which don't roll well) as well as all of the other stuff we take (autograph books, pin trading lanyards, glow bracelets, etc) we usually end up taking a small and large bag, or two small bags instead. Even with tightly packing our large bag with space bags and other assorted stuff, we have a hard time getting it over 40lbs (SWA's limit is 50).
The travel bags you roll instead of vacuum. They have a one-way valve system at the far end that allows air out but not back in again. We also have some dual-use bags that have both that and the vacuum attachment. They work great for us! And we've never had a problem with TSA.
Amanda