First of all, it is quite larger than it appears. In the photo showing it on a bike, the bike is at least an XL frame with 29" wheels. So if you have a Large or Medium frame, expect that it will take up more space and you won't be able to fit a water bottle underneath. On my Specialized Rockhopper Large size, it doesn't fit a water bottle underneath unless I push it and crumple the bag in the front corner. Inside, there are no pockets or clips for keys; it is just a plain single space, so if you put in a few items, they will bounce around a bit in potholes/uneven terrain. Another downside is that it is not 100% waterproof. With the zipper closed and hidden, I rinsed the bike with just water and found half a shot glass worth of water inside the bag. On the positive side, it has enough space for a small pump, spare tube, wallet, phone, etc., but everything is just loose inside. Its most positive point is that it is indeed perfectly stable, as its straps are long, strong, and have anti-slip material inside, so if you place it correctly, the bag doesn't move a millimeter; it becomes one with the bike! If you get caught in a downpour on the road, I don't think it will take in water, but I haven't tested it yet to know how much rain it can withstand. The material is quite thick, so I'm not worried about it tearing, and the zipper also seems to be of good quality. If it had at least one pocket, even a mesh one like others, and hadn't let in some water during washing, I would easily give it 5 stars. So in my opinion, it is better for racing and not for mountain bikes, unless you don't mind everything you put inside bouncing around like a frappé. For gloves, wallet, spare tube, mini-pump, it is ideal. For phones, flashlights, etc., not so much.