I do use slimfast but more because it a nice alternative to chocolate milk and it has vitamins and stuff added and sometimes I just really enjoy having one and them satisfying.
If you want to go that route, I would recommend instead a high quality whey protein, like they sell at GNC. They come in many different flavors. Make with water, or you can make with milk for additional protein. Blend in some fruit (like a banana) and you've got more a shake than a drink. More filling.
I like to add slim-fast in especially when I am not hungry, but need to eat so that I am not "starving" later, know what I mean? I find them to be really filling for a minimal amount of POINTS.
I used a chocolate flavored whey protein powder I got at Trader Joe's, mixed with a cup of skim milk and it is 5 points, with only 2 or 3 grams of fat (I can't remember right now) and 26 grams of protein.