I don't understand. They aren't diluting shares, they aren't liable if the company fails to reach Series A, and by all accounts there do not seem to be any strings attached with regard to oversight (ie. the founders don't need to "answer to" the investor in any way). All they are doing is giving a portion of their future shares to that investor now, at the same value as they would later. It's a no-brainer - what is the downside in your opinion?