I've used one. I still do for mountain biking. Not a big fan for road biking. For the road they are a bit heavy and place weight on your back when you are in a crouch. They are hot. The water is often warm and sometimes has a taste. I find I don't need all the storage for road biking. For mountain biking you need more storage and the weight on your back is better distributed onto your shoulders. They are still hot for the up hills and the water can get warm and a bit funky. The better ones have a bit more insulation for the water bladder.