Where 'the hype' includes claims of total meal replacement over long periods of time.. yes.
I don't think many, if any, people are concerned that this stuff is literally toxic. The concern is what will happen if you use it as advertised: constantly, exclusively, for extended periods of time.
People eating McDonalds for every meal every day of the week is troubling, I don't think anybody actually suggests you do that. McDonalds certainly doesn't suggest that you do that, though I sometimes feel that many people wish they did suggest you do that so that McDonalds would be easier to flay alive. Being appalled by McDonalds is an international sport after all...
There really isn't that much of a problem with eating a greasy deep-fried cheeseburger once in a while, and there isn't a problem with skipping a meal or two and having a shake instead. That isn't what concerns me, that isn't what seems to concern DanBC ("I think that's the worrying thing about Soylent. I really wish they'd kept it experimental, or pushed it as suitable for daily use but not all meals, or some such."), and that isn't what I see concerning other people in this thread. The literal product, the substance Solyent, is almost certainly perfectly fine to consume. So are cheeseburgers.