I did a ton of research on seat bags. I have no life. After putting way too much time and thought into something as simple as a seat bag, I decided to go with this small, simple and clean bag. I guess some of the photos were a little misleading as to the petite size of this thing, but man it's tiny! The nice thing is, you can still pack quite a bit to help you get home in case of a flat. One of the main reasons I took so long to pull the trigger on a bag is because I know they are generally shunned as being ugly and stupid...but they still serve a very important purpose! Often times I'm riding before I work the evening shift and I will go for 20+ miles away from home during the middle of the day when most people are at work, that means if I get a flat, I'm stranded.
I have this stuffed with 1 tube, tube patches, a Pedro tire lever (pretty bulky), a 6 tool mini-tool, 1 x Co2 cartridge and Planet Bikes Co2 chuck (The one with that big red knob which is obnoxiously huge! Don't buy it). It all fits rather well and still zips just fine.
I ended up also purchasing the Arundel Dual from Competitive Cyclist because I ride some rough roads, dirty trails, and generally have bad luck. This will hold 2 tubes and Co2 cartridges plus a larger multi tool which gives me enough confidence to ride harder and farther before I have to go to work.