Wouldn't recommend these fad diets. The reason why dieting companies are so lucrative is that they rely a high relapse rate...otherwise they would be out of business.
Also consuming very low calories will slow your metabolism, therefore you will find it harder to lose weight. You put your body in starvation mode and once you go back to eating normally, you will gain weight back even faster. Furthermore, you are missing out on key nutrients which you need for your body to function properly by being so restrictive.
It's much better to eat healthily and exercise regularly. Being healthy is a long-term lifestyle choice. It's not a quick fix. Yes it's hard, which is why many don't do it and seek quick fixes...and ultimately fail. Eat fresh and nutrient dense foods (80% of your diet should be this) and exercise four of five days of the week. You'll keep the weight off this way and be much healthier.