You couldn't live on SlimFast if you had to. It's an appetite suppressant/meal replacement for short term use, given that it's not nutritionally balanced.

Neither is it similar to Ensure or most other meal replacement drinks for the same reasons. They're usually absolutely loaded with fast, low-index sugars that'll spike your blood sugar.

Basically, it's the food equivalent of water. Neutral, nutritious, has what your body needs and nothing more. The carb source they're using is high-GI, meaning it won't cause that spike. The idea being that when you CBA'd to cook, when you'd normally run to the local burger joint's drivethru, you shake up a glass of this stuff, and you're back to doing whatever you're doing for cheaper (about $3 a meal) and in less time.

Basically, it hits all of the right notes that most of the on-the-shelf competitors do not. It's relatively cheap, it keeps a long time, it's actually good for you, it's convenient as food could ever possibly be.

I personally love the stuff.