I just used these on a cross-country trip. The cubes are very good quality - I didn't have any problem with the zippers, even after 3,000 miles.  This was the first time I had ever used packing cubes.  I used the "rolling" method instead of folding my clothes.  I was amazed at how much I could fit in my suitcase with these cubes.  I should have bought them a long time ago.