I tried it once ages ago and I must admit it did seem to be doing something, but I was exercising vigorously and eating really clean as well. It does make you feel really weird though. Like you are totally hyped up all the time. Your pupils get diallated and you feel like you are clenching your teeth all the time. Must be all the caffeine and guarana in there.
The thing that I would say about all these weight loss supplements is that even if they do work, once you stop using them you are going to have to work twice as hard not to put the weight back on. It's an unnatural way to lose weight and it doesn't teach you any long term healthy eating habits.
I would definitely not recommend it.