The major problem is that most of them taste like lightly flavored motor oil. The Myoplex though is okay...provided you jazz it up with fruit and milk or yogurt. I generally make it with water, throw in whatever fruit I have on hand, and add a small container of fat-free frozen yogurt. It's quick, it's easy, and actually tastes comparable to a milk shake. There is an added bonus that the stuff is loaded with vitamins and minerals. It also has a lot of fiber which is good, but gives you the side effect of cutting some ferocious farts later in the day...so you may have to time your interactions with others.
Quick, portable, and easy, no cooking required
Nutritious and satisfies hunger
As far as supplemental shakes go, it is actually good tasting
Requires a blender
Not great but not bad. Real food is always better but you can't always get real food. These meal replacement shakes help me from eating other things when I'm hungry so that I can stay on track in my diet aims.