How much anyone loses depends on how overweight they are to start with, how tall they are, and how active day to day. Also, if you have already been dieting on another plan before starting this diet, you may not lose as much as you would if you hadn't dieted for a while.
Since this diet is low carb and pretty low calorie too you should lose a lot the first week - 7 pounds, perhaps, or a bit more or less. If you have a lot of weight to shift you could lose 10 pounds or more.
Bear in mind that the second week losses will be less because most of the first week losses are water. Even so water has to go somewhere in the body and it bloats us and takes up room! Losing that surplus water will make you look and feel much slimmer.
I am a longtime low carber (vegetarian Atkins) and this suits me very well. I have used dietimeal/protimeal products many times - exactly the same as celebrity slim - and had good results. But watch out cos not all the products are total meal replacements! You don't want to go short of nutrition.
Good luck! x