I don't think people that grab onto this stuff are gullible, more they are desperate to have an easy solution to something that is very difficult. They truly want to lose weight and have the desire to lose it, but they don't want to put the effort and hard, really hard work it takes to accomplish a permanent solution.
The trouble with anything that you put in your mouth, wear on your body or whatever is that most overweight people don't know how to control food or why they it eat. I don't care whether you have gastric bypass and lose 300 lbs or take Dexitrim and lose 5 lbs, if you don't learn what makes you eat what and when you aren't supposed to, it is all for naught. It is like all other addictions in life, if you don't control it, it controls you. You may be an anger eater, stress eater, happy eater, busy eater or a myriad of other things, but until you get a permanent handle on what triggers you to eat when you aren't really hungry you will never keep the weight off and yoyo your whole life. It isn't an easy thing, but than nothing that is truly important in life ever is!