If you have a Fizik saddle then I would recommend their bag. It clips under the saddle and can be moved to other bikes in a second. I had one break at the plastic mount but was replaced under warranty by my LBS. I love these as there is no straps to wear through my nice carbon seat post. I have the small one and it fits two tire levers, a tube, small multi-tool, patch kit, 2 CO2 cartridges and nozzle, nitroglycerin and dog tags.