Sorry to have resurrected this thread from 7 years ago, but in case anyone is still interested in this and found this thread on Google, like I did, I'd like to offer my two cents. This Office Bag from Topeak is excellent. It comfortably holds a 1.5" binder, 15" laptop, and other school/office supplies, and fits securely on my MTX QuickTrack rack and BeamRack. Unfortunately, it seems as though this product is no longer being manufactured, and is largely unavailable except for the link you provided at a ridiculous markup. I'd better make sure to take good care of mine, because unless they bring this back or update it with a new model, I'll have to go back to using a backpack again. Or get normal panniers, because the Explorer EXP (or whatever it's called) trunk bag with expandable panniers, while spacious and convenient, is not easy to carry around and access in class or at the office.