I'm still satisfied with the Serfas Speed Bag after about six weeks. Functional, looks good, lots of nice little niches and details for organizing small items, highly reflective strips, external loops for attaching a taillight or other doodads.

I got the medium with expandable bottom since occasionally I need to stuff the Topeak RaceRocket HP inside when I switch the bag to my hybrid (no bottle cage mount for the pump). Holds everything I need, although I tend to overpack on longer casual rides. The expansion makes room for a USB battery pack and cords, extra snacks, small Olympus digicam, etc. Handy on rides when I'm not wearing a jersey with rear pockets.

Only nit I'd pick is pretty minor, but I wouldn't object if Serfas redesigned the two Velcro straps that hook over the saddle rails. It's not a bad design, just a bit fussy. I have to poke my fingers inside the little space between the rails and bottom of the saddle to snug it up. But the strap ends are tucked under the saddle rather than rubbing my legs.

It swings a little bit but so do most similar bags. I don't notice when I'm riding. If that bothered me I'd get a clamshell type.

I checked every commonly stocked saddle bag for months -- Topeak, Arundel, Jandd, etc. -- and didn't find anything I liked better than the Serfas Speed Bag. And Serfas makes others that are narrower and lighter but essentially similar designs.