i have both the largest of those topeak expandable bags (for groceries and bike n hikes) and the smallest one (for daily commuting.

i've had both for a couple of years now. i bought the larger one first and used it for day to day commuting (rain and snow and mud) before deciding it was overkill for most days and buying the smaller one.

both of them have been through the wringer, and been beat to hell but both are mechanically brand new. theyre dirty as hell, but no frayed fabric or busted zippers or worn our edges, and the springs and latch on the rack attachment are in perfect shape.

http://luttet.net/pics/bike_commute_pics_004.jpg

highly recommended.