i have used just about every "fat burner" out there and done extensive logs on them keeping track of my weight and body fat. i can tell you that 99.9% of them will make you lose weight, will make you feel more energy BUT if your diet isnt dialed in, as soon as you go off of them, you are quickly back to where you started. if your diet isnt right, you will burn muscle and not fat! if you arent into a good solid workout program, you will burn muscle and not fat. i used a very intensive "fat burner" when i first got back into the gym and i took weekly pics, weekly weight, weekly body fat, weekly measurements. it was a 3 month program. i was NOT eating very good. yes, less than i had been but i was using the "fat burner" as a crutch so i was still eating a lot of stuff that i shouldnt be and my calories were still too high. at the end of the 3 months i had lost about 10# and my measurements had dropped some but my bodyfat, increased. not a whole bunch, like 1% but it went up and my muscle mass went down. so yep, i was 10# lighter, my lifting sucked and i still looked the same because the amount of fat was pretty much the same. had the same results a year later when i did a log on another "fat burner" lost 10# in 6 weeks and in 2 weeks after i was done i was right back at my beginning weight.
so if you want to take them to make you feel better and get that energy, go for it. i take an animal cuts package every morning about 10ish when i start to feel tired. i have every intention of trying GGs product when he gets it out there but my diet is much better than it used to be.
"fat burners" are a tool but they are not going to fix or overcome ones bad diet.