I bought a pair of these many years ago 'as seen on tv'. The plastic was fairly thick and they still serve today. A couple years ago I bought the set harborFreight offers and they were a similar thickness and they also work fine. I examined a set at some other low-budget department store (might have been KMart) and they were much thinner. More like those thin vinyl bags toy soldiers used to come in.
They're very inexpensive, certainly worth a try if you are considering these things
http://www.harborfreight.com/3-pack-vacuum-storage-bags-95613.html
eta those ziploc bags look nice, but at 4x the unit price they'd better be.
eta2 either way, a compression bag would be a good way to store some road emergency blankets or other cold-weather gear in case of a vehicle breakdown, or some other similar purpose. Compressible fabric gear you MIGHT need, vs WILL need.