Russell Brand doesn't claim to be an economist. Let's face it, most of these "experts" did not foresee the near collapse of the financial system and now seem perplexed that the current economic situation doesn't conform to their text book models. Some would also argue that they are complicit in maintaining a system that is unfit for purpose in that it only benefits a tiny proportion of the world's population.
Although some of Russell Brand's views seem outlandish, he is at least interested in the issues of injustice and inequality and perhaps he has encouraged young people to take more interest in what is happening in the world today.
It's interesting that most people who are rubbishing his ideas, have not read his book and are forming their opinions courtesy of the mainstream media. When I've read his book, I may also come to the conclusion that it's utter nonsense, but until I have I'll reserve judgment.