I'm using the Ideal Protein plan and am steadily losing weight. 40 lbs. in 4 months so far. This is the second time I've been on it. The first time it worked also, but I quit because I was eating for emotional reasons, not hunger. No fault of the plan.
It's a deliberately unbalanced diet: no carbs (that is, no sugar, breads or fruit), adequate protein to maintain muscle mass, adequate fat for liver health, 64 ounces of water daily, and very specific vitamins and minerals. After you lose the weight you go back to a balanced diet, emphasizing a healthy attitude toward food as a forever lifestyle, with the help of your coach.
If you follow it 100% it works 100%. If you follow it 95% with "just a couple" cheats here and there, it will not work. You have to make a choice. (As with so many things in life.)
It's expensive. As McBain II says, you can do it on your own at a fraction of the price. But will you? That's the question. For me, having the correct nutrition in packet form is such a no-brainer that I can follow it effortlessly. And I didn't have to become a nutritionist to design my own plan. I'm never hungry. My inflammation is gone. I don't have indigestion, acid reflux, or the roller coaster sugar highs/lows. I sleep well. And my energy is increasing by the week.
This is my experience. The only way I could be happier is if I didn't have the personal failings that prompted me to become fat in the first place.