FairSoftware's virtual deal only works for peer-to-peer, meaning both need to be private individuals entering into a co-founder deal, not an outsourcing agency and an LLC for instance
If the other party is unknown, a strength of the product is that there is a one-month trial period : if the relationship doesn't work out after 1 month, you can kick the other person out and it's as if the relationship never existed (of course, you then have to return any contribution by the person you kicked out)
After that one month, the system automatically enforces vesting, so that if you feel the relationship is eventually going south, you only give away the equity up to that point. And there is not arguing over it (which otherwise would get ugly), because it's all built-in.
-- disclaimer: I'm one of the co-founders of FairSoftware