It's a really nicely made bag, but I couldn't fit it to a men's or women's bike. To get the bracket and clip on the bag to meet, the bracket needs to be as far back on the saddle rails as possible. On both the saddles I tried the rails weren't close enough together at that point and so the bracket wouldn't stay in place. Replaced with the bag with standard version and much happier. Sigma were really helpful.

I bought the medium size and it is just right for what I wanted to fit into it - 2 spares tubes, a puncture repair kit and a multi tool; there is even a little roon for a couple of gels or cereal bars but you'd have to omit one of the tubes to get a phone in there. The quick release clip was easy to fit to the saddle rails and goes on and off easily - great for when you stop and want to remove the bag. The ability to attach a clip on light is good as the seat post is fairly well covered when the bag is fitted. The bag seems to be robustly made but only time will tell. The aero shape fairs in nicely under the seat and you'd never know it was there. I ordered this and the large size (not quick release) with reserve and collect (great feature from Sigme) and choose the medium size as the large looked a bit big for what I wanted. Really good price too so not a dissaster if you need to buy another size in the future. Just a shame it is not waterproof