He plans to use some of the money to run formal clinical trials.
Promissory notes and jam tomorrow.
As of 2015, even the vague pious hope of trials seems to have been long abandoned; apparently Rhinehart & Soylent are quite busy merely shipping and keeping things running...
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.