Like many here, I keep an eye on calories and exercise. It's slow going, but for the first time in my life it's working. If I can do it, anyone can.
I have a good friend who was doing Lighter Life. She had great success with it, for a time, then found that the low calorie regime was too hard to take, she got ill, and had to return to food. 18 months on I have lost twice as much as she did, whilst taking in twice as many calories
I think if you are realistic about what you are getting in to, then a very low calorie plan can work fine. But you will need to return to food at some point, and unless you are very disciplined, may find it hard to maintain your loss without the rigidity of the program.
I'd find out just how much you are committed to up front, and whether you can get a refund if you drop out.
Have you spoken to your gp about your weight? Are you obese? In the UK now your gp is obligated to help you if you fall into the obese category.
I would urge you to do this before you give any serious pounds to anyone who stands to make a lot of money out of you!