Apologies for another thread about panniers, but I have no way of trying these before buying. Dimensions for these two are listed as the same, but the shopper has a zipper seam. Does that mean the effective size is bigger because no rolling down needed? Advantages/disadvantages of the two? I need something that can fit a folded dress shirt loosely so no wrinkles. And lunch, etc. really want the quality of the ortlieb attachment. Thanks for any thoughts.