Soylent can claim what they wish. When it comes to my health, I think I'm going to hedge towards the side that doesn't purport to be everything your body needs for nutrition in powder form, crafted by people with little nutritional science background.
purport: appear or claim to be or do something, especially falsely; profess.
Would you choose the guy who _purports_ to be an electrician, or the guy who _is_ a licensed electrician?
I wouldn't hire either without seeing some legitimate qualifications.
That they don't advertise to the general public; or don't say "you can live off this and nothing else" says something about Soylent's unethical marketing.
The Ensure range is easiest to get hold of for the general public. (Ensure and Ensure Plus are sometimes used as sole source nutrition in forced NG tube feeding for hunger-striking prisoners or eating disordered patients.)
Now there's a good brand differentiator...hang on, I have a Wikipedia page to improve.
(EDIT: I don't know why you're being downvoted. I upvoted you to try to correct that.)