I just got back from a multi day mountain biking trip. I went over a great deal of bumpy terrain and this bag and rack did not budge. As for space, in the main compartment it easily held three days worth of bike clothes (jerseys, shorts, socks), a couple of t shirts, two pairs of shorts, flip flops, hygiene items, and three snack packs in sandwich sized ziplock bags. The side, rear and top pockets are also very spacious. Oftentimes with bike bags the outside pockets are almost useless, but not with this bag. The two side pockets easily held my tools (shock air pump, spare 26x2" tube, multi use tool, knife, chain tool, chain links, bottle of chain lube w/ rag, tire levers, bike lock, etc.). The bungee on the top of the bag is also useful as it held my sleeping bag liner and a light rain jacket for easy access. I wanted to keep as much weight off my back as possible. All I had to have in my backpack were my two hydration bladders.As others have mentioned, the ride dynamics do change a bit with this bag as likely with any other rear bike bags. I didn't do any practice rides with this bag fully loaded, but I didn't have an issue. You just need to be more cautious when going downhill with more weight centered over your rear wheel. But with no practice prior to the trip, I was fine and it wasn't an issue. I wouldn't suggest doing real technical riding with this bag, but I rode some nice single track without an issue. I had the rack mounted at the base of my seat post and you do have to lift your leg a little higher to get seated, but it wasn't an issue for me.Overall the bag and frame are made of high quality materials and the main compartment and pockets are perfectly designed. The zippers are high quality as well. The rack itself is lightweight so there is obvious weight savings there compared to a typical pannier rack that screws into the frame.Another reviewer mentioned there should be a strap integrated on top of the bag. I found that if the bag had a strap on top, you'd lose storage on top with the net. There is a strap included that when tightened all the way acts as a hand strap or your can loosen it and carry it over your shoulder. Either way the strap comes on and off and you at least have some choices how you want to use it.The bag easily clicks in and out of the rack which was useful for short stops during the trip. One of my friends on the trip (who is not easily impressed) had most of his gear in his backpack and he looked over at me after I unclipped the bag and he said "it unclips too? Nice". Overall I wouldn't change anything about this bag. It's perfect. This is one of the best products I've purchased off Amazon. For the price the value is hard to beat. Most manufacturers/retailers charge the same price just for the bag without a rack.