This is a great bag as it has plenty of room to put your keys, bike tools and other misc items and you still have a place on the outside for an extra water bottle. It has two straps for the seat post and two that attach to the seat. The Velcro is very strong and holds the bag in place even on the roughest terrain. I was afraid that the bag would be too tall to fit between my seat and the brake but it actually fit very nicely. I like the reflective strips on the side but it would have been great if there was a strip on the back as well, you can never stand out too much to cars behind you. I love that the inside of the bag is a nice bright orange color so when you open it you can see your items inside pretty clearly. I really wish there were different color options for the stripe on the side but other than that I love this bag. The water bottle does not come with the bag it is one I got from Bicycling Magazine when I signed up for a subscription.