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.
Slim Fast:
http://www.livestrong.com/article/125563-slim-fast/
http://www.fathead-movie.com/images/slimfast.png
https://tamafitness.files.wordpress.com/2011/08/shakeology_v...
Sounds like you could probably survive entirely on Slim Fast. It's got Iron (which the original Soylent didn't have), Vitamin A, Vitamin C, Vitamin B, Vitamin D, and Iodine, and a bunch of other micronutrients. You probably wouldn't have a great time but I doubt you would on a Soylent-only diet either.
Solyent doesn't seem to differ much:
http://files.soylent.com/pdf/soylent-drink-nutrition-facts-e...
Slimfast is a diet drink as the name implies, while Soylent is a meal replacement. If you wanted to get a reasonable (non-starvation) amount of calories from Slimfast to live on it and it alone, Soylent then wins on balance and cost.
They also seem to have a protein shake drink http://d8m5oga7foiu.cloudfront.net/wp-content/uploads/2016/1... which seems similar but obviously lower in calories, better protein:carb ratio though. They also seem to sell some powder you can mix with milk, presumably you could put more than one scoop in.
Not saying Solyent doesn't work for you and I don't want to sound like I'm promoting Slimfast. It's just not the first or only meal replacement shake.
Really? Slimfast and Ensure have much higher amounts of sugar; what are you thinking of?