This kit comes with a brush for the reservoir and a brush for the hose. The brush for the bladder is not that essential; just about any kitchen scrub brush with a handle will do. But finding a long and skinny tube brush can be a pain. The main reason to buy this kit is for the tube brush.
For another $10, you can get the Antidote Cleaning Kit that includes a drying rack and bacteria-killing tabs.
Why do you even need a cleaning kit and how often do you need to use it? We answer this question and more in our article How to Choose a Hydration Pack and our Hydration Pack Review.