The Thule is solid. Because the rack is so narrow, it's not a perfect fit. Back and front attaches Velcro or slide one end to the front or back of rack and just use use two Velcro straps instead of 4. It's big enough for huge U-Lock and heavy duty chain, portable bike pump, tools, tablet, phone, wallet and a couple of bottles of beverages. It's cool bag for riding around town, or taking bike on the train. Carries like a briefcase. Personally, I think it's overpriced ($87) but at the time I didn't see any other options. Doesn't move around on the rack. Pretty snug, but not as snug as the Ortlieb bags that fit perfectly with your own reducer. The 8mm and 11mm didn't work for me. I made my own out of some rubber pieces I had laying around. I cut them with a blade and crazy glued them inside the parts that attach to the top of the racks. Perfect fit. On and off super easy.