I have seen mixed reviews on this and personally they have worked wonders for me. Everyone reacts differently so this is just based on my own experience.
I eat a very good diet, six meals a day consuming over 3500 calories a day, drink at least 2.5 ltrs of water a day. For me it was to cut the last bit of lower stomach fat to get the abs showing. Not taking this to loose weight so I have upped my calorie intake as a result to closer to 4000. After two weeks I look a lot leaner than I have ever done before. For cutting, this is a great product!
I have been taking the recommended dosage with my last dose at 6pm. I have not had any side affects, especially consdering prior to this I did not have caffine in my diet. I only drink water and the very occasional freshly squeeezed orange juice. The levels of caffine went from zero to astromonical and did not feel anything. I have not had any anxiety attacks, nor sleep deprivation.
I will most likely do cycles of 3 weeks and than 1 or 2 months off. I would not hesitate to recommend this but if you are apprenhensive or have any medical conditions, do consult a doctor. Also do your research prior to starting on these. These do not work on their own, they are supposed to be taken with an adequate regime and diet plan. It works for some and does not for others, it is all trial and error although fairly expensive at the same time. Give it a whirl and see if it works for you.