This is a great little bag. I prefer the small size, just big enough to carry a tube, inflator, a couple of cartridges, and a tire iron. If you need to carry more, go for the medium.....
It is the perfect size to fit under all of my saddles, including for mountain, road, and time trial bike saddles. Not only does it hold all essential repair equipment, it is also perfect for added safety through its integrated reflective fabric.
I wanted this bag because my old one had velco that kept grabbing onto my shorts and eventually ripping them. This bag has an adjustable strap which is much better. Fits nicely under my seat, and holds all I need it to hold. Wish it had an inside pocket. Seems durable, but have not had to to long.