I use them for breakfast. I am not a breakfast person, and never have been, which is a bad habit for me to break, but I needed to have something in the mornings. I find eating just turns me off, and the shake for me are a good way to get a meal without feeling like I am eating.
You really have to read the backs (nut. panel) as some can be a little high in Cal's. I mix mine with water, although you can use milk, but I find water works fine. I also keep one in the car now in my glove box if I get stuck out and about, all I have to do is mix it up in the bottle.
I think if you rely on them to loose weight the weight will fall off, but my sister-in-law did it that way and after the shakes she but all 26 kg plus more back on.
Lifestyle change should be the focus for perm. lose.
But like all weightloss methods - Each to their own