I bought some a few weeks ago while out sourcing ingredients for some DIY soylent.
It was disgusting.
Ensure Complete has an interesting nutrition panel: it's 25% of everything listed, if I remember correctly. A four pack is 1400 calories and everything you need for a day. In my local stores, it's about $8. Jevity isn't marketed in grocers like Ensure Complete is.
You don't. If you tried to live on ensure complete (which they seem to only sell in the US?) you need to add potassium, choline, more fat, more calories in general, more fiber, more sodium and chloride, but unfortunately not in the ratio they are found in salt (that was bright) and you now have diarrhea all the time from the magnesium. All that and it is more expensive than soylent. This crap is precisely why people are stoked about soylent, we've tried the existing products and they suck.
http://abbottstore.com/adult-nutrition/ensure-complete-milk-...
But, this crap is not why people are stoked about soylent, since the vast majority of people who are excited about soylent don't seem to be aware that there are a bunch of products that are pretty close (or possibly better in some cases) already.